Remove -Werror flag from build

Buck refuses to build with at least one version of OpenJDK 7,
complaining about a number of Paths APIs being deprecated.
diff --git a/build.xml b/build.xml
index 0125614..e746c17 100644
--- a/build.xml
+++ b/build.xml
@@ -92,7 +92,6 @@
            >
       <compilerarg value="-Xlint:rawtypes" />
       <compilerarg value="-Xlint:unchecked" />
-      <compilerarg value="-Werror" />
     </javac>
   </target>
 
@@ -105,7 +104,6 @@
            >
       <compilerarg value="-Xlint:rawtypes" />
       <compilerarg value="-Xlint:unchecked" />
-      <compilerarg value="-Werror" />
     </javac>
   </target>
 
@@ -126,7 +124,6 @@
       <exclude name="com/facebook/buck/java/abi/**" />
       <compilerarg value="-Xlint:rawtypes" />
       <compilerarg value="-Xlint:unchecked" />
-      <compilerarg value="-Werror" />
     </javac>
   </target>
 
@@ -177,7 +174,6 @@
            >
       <compilerarg value="-Xlint:rawtypes" />
       <compilerarg value="-Xlint:unchecked" />
-      <compilerarg value="-Werror" />
     </javac>
   </target>