Add variable support to Transformation.opacity() (#209)

Author: nitzanj

cloudinary-core/src/main/java/com/cloudinary/Transformation.java

@@ -202,7 +202,7 @@ public T delay(Object value) {
         return param("delay", value);
     }
 
-    public T opacity(int value) {
+    public T opacity(Object value) {
         return param("opacity", value);
     }
 

cloudinary-core/src/test/java/com/cloudinary/test/CloudinaryTest.java

@@ -527,6 +527,10 @@ public void testOpacity() {
         Transformation transformation = new Transformation().opacity(50);
         String result = cloudinary.url().transformation(transformation).generate("test");
         assertEquals(DEFAULT_UPLOAD_PATH + "o_50/test", result);
+
+        transformation = new Transformation().opacity("$var");
+        result = cloudinary.url().transformation(transformation).generate("test");
+        assertEquals(DEFAULT_UPLOAD_PATH + "o_$var/test", result);
     }
 
     @SuppressWarnings("unchecked")