Fix SimpleModuleVersionIdentifier.toString() not including extension when needed

Author: LexManos

gradleutils-shared/src/main/java/net/minecraftforge/gradleutils/shared/SharedUtil.java

@@ -389,7 +389,7 @@ public String toString() {
             if (classifier != null)
                 builder.append(':').append(classifier);
 
-            if ("jar".equals(extension))
+            if (!"jar".equals(extension))
                 builder.append('@').append(extension);
 
             return builder.toString();