Workaround for error in groovydoc task (grails#53)

* Prevent groovydoc error by using explicit type arguments instead of
  diamond operator
* Revert once a fix for GROOVY-8628 is included in groovy dependency

src/main/groovy/grails/plugin/cache/GrailsConcurrentLinkedMapCache.java

@@ -44,7 +44,9 @@ public GrailsConcurrentLinkedMapCache(String name, long capacity, boolean allowN
       this.name = name;
       this.capacity = capacity;
       this.allowNullValues = allowNullValues;
-      this.store = new ConcurrentLinkedHashMap.Builder<>()
+      // Workaround: using explicit type arguments to prevent groovydoc error (#53)
+      // Replace with diamond operator once a fix for GROOVY-8628 is included in groovy dependency
+      this.store = new ConcurrentLinkedHashMap.Builder<Object, Object>()
          .maximumWeightedCapacity(capacity)
          .build();
    }