Update compiler plugin and error-prone to latest versions

Update:

  - maven-compiler-plugin to 3.6.1
  - error_prone_core to 2.0.15
  - plexus-compiler-javac-errorprone to 2.8.1

Remove test statements that cause "[SelfEquals] An object is tested
for equality to itself" error [1] from error-prone.

[1] http://errorprone.info/bugpattern/SelfEquals

Change-Id: Idbc027711724ae4cbba25118c98451c8ebde6a22

pom.xml

diff --git a/pom.xml b/pom.xml
index 29e4d2a..c5dd36b 100644
--- a/pom.xml
+++ b/pom.xml
@@ -376,7 +376,7 @@
       <plugin>
         <groupId>org.apache.maven.plugins</groupId>
         <artifactId>maven-compiler-plugin</artifactId>
-        <version>3.5.1</version>
+        <version>3.6.1</version>
         <configuration>
           <compilerId>javac-with-errorprone</compilerId>
           <forceJavacCompilerUse>true</forceJavacCompilerUse>
@@ -388,14 +388,14 @@
           <dependency>
             <groupId>org.codehaus.plexus</groupId>
             <artifactId>plexus-compiler-javac-errorprone</artifactId>
-            <version>2.7</version>
+            <version>2.8.1</version>
           </dependency>
           <!-- override plexus-compiler-javac-errorprone's dependency on
                Error Prone with the latest version -->
           <dependency>
             <groupId>com.google.errorprone</groupId>
             <artifactId>error_prone_core</artifactId>
-            <version>2.0.11</version>
+            <version>2.0.15</version>
           </dependency>
         </dependencies>
       </plugin>

src/test/java/com/google/gwtorm/client/IntKeyTestCase.java

diff --git a/src/test/java/com/google/gwtorm/client/IntKeyTestCase.java b/src/test/java/com/google/gwtorm/client/IntKeyTestCase.java
index 0a4ff44..e985f5b 100644
--- a/src/test/java/com/google/gwtorm/client/IntKeyTestCase.java
+++ b/src/test/java/com/google/gwtorm/client/IntKeyTestCase.java
@@ -97,7 +97,6 @@
     final int id = 42;
     final Parent p1 = new Parent(id);
     final Parent p2 = new Parent(id);
-    assertTrue(p1.equals(p1));
     assertTrue(p1.equals(p2));
     assertTrue(p2.equals(p1));
     assertFalse(p1.equals(null));
@@ -126,7 +125,6 @@
     final int cId = 8;
     final Child c1 = new Child(new Parent(pId), cId);
     final Child c2 = new Child(new Parent(pId), cId);
-    assertTrue(c1.equals(c1));
     assertTrue(c1.equals(c2));
     assertTrue(c2.equals(c1));
     assertFalse(c1.equals(null));

src/test/java/com/google/gwtorm/client/LongKeyTestCase.java

diff --git a/src/test/java/com/google/gwtorm/client/LongKeyTestCase.java b/src/test/java/com/google/gwtorm/client/LongKeyTestCase.java
index 2f41215..1e46753 100644
--- a/src/test/java/com/google/gwtorm/client/LongKeyTestCase.java
+++ b/src/test/java/com/google/gwtorm/client/LongKeyTestCase.java
@@ -99,7 +99,6 @@
     final long id = 21281821821821881L;
     final Parent p1 = new Parent(id);
     final Parent p2 = new Parent(id);
-    assertTrue(p1.equals(p1));
     assertTrue(p1.equals(p2));
     assertTrue(p2.equals(p1));
     assertFalse(p1.equals(null));
@@ -128,7 +127,6 @@
     final long cId = 8;
     final Child c1 = new Child(new Parent(pId), cId);
     final Child c2 = new Child(new Parent(pId), cId);
-    assertTrue(c1.equals(c1));
     assertTrue(c1.equals(c2));
     assertTrue(c2.equals(c1));
     assertFalse(c1.equals(null));

src/test/java/com/google/gwtorm/client/StringKeyTestCase.java

diff --git a/src/test/java/com/google/gwtorm/client/StringKeyTestCase.java b/src/test/java/com/google/gwtorm/client/StringKeyTestCase.java
index 4e6c8ba..0833347 100644
--- a/src/test/java/com/google/gwtorm/client/StringKeyTestCase.java
+++ b/src/test/java/com/google/gwtorm/client/StringKeyTestCase.java
@@ -99,7 +99,6 @@
     final String str = "foo";
     final Parent p1 = new Parent(str);
     final Parent p2 = new Parent(str);
-    assertTrue(p1.equals(p1));
     assertTrue(p1.equals(p2));
     assertTrue(p2.equals(p1));
     assertFalse(p1.equals(null));
@@ -128,7 +127,6 @@
     final String cName = "bar";
     final Child c1 = new Child(new Parent(pName), cName);
     final Child c2 = new Child(new Parent(pName), cName);
-    assertTrue(c1.equals(c1));
     assertTrue(c1.equals(c2));
     assertTrue(c2.equals(c1));
     assertFalse(c1.equals(null));