Omit optional =true when using /diff?weblinks-only

The addParameterTrue() method packs the request parameter with no
argument, which the REST API server understands to mean a boolean
true value. This is consistent with most other options throughout
the API.

Change-Id: Ia69bb60b3fe6ee8858066642bb239ed5df664225
diff --git a/gerrit-gwtui/src/main/java/com/google/gerrit/client/diff/DiffApi.java b/gerrit-gwtui/src/main/java/com/google/gerrit/client/diff/DiffApi.java
index 321883d..18d673a 100644
--- a/gerrit-gwtui/src/main/java/com/google/gerrit/client/diff/DiffApi.java
+++ b/gerrit-gwtui/src/main/java/com/google/gerrit/client/diff/DiffApi.java
@@ -64,7 +64,7 @@
   }
 
   public DiffApi webLinksOnly() {
-    call.addParameter("weblinks-only", true);
+    call.addParameterTrue("weblinks-only");
     return this;
   }