Fix normalize_expression when a keyword is used in a variable name (#205)

Author: RTLcoil

cloudinary-core/src/main/java/com/cloudinary/transformation/BaseExpression.java

@@ -107,7 +107,7 @@ private static Pattern getPattern() {
             sb.append(Pattern.quote(op)).append("|");
         }
         sb.deleteCharAt(sb.length() - 1);
-        sb.append(")(?=[ _])|").append(StringUtils.join(PREDEFINED_VARS.keySet(), "|")).append(")");
+        sb.append(")(?=[ _])|(?<!\\$)(").append(StringUtils.join(PREDEFINED_VARS.keySet(), "|")).append("))");
         pattern = sb.toString();
         return Pattern.compile(pattern);
     }

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

@@ -218,4 +218,14 @@ public void testShouldSupportPowOperator() {
 
         assertEquals("$small_150,$big_$small_pow_1.5", t.generate());
     }
+
+    @Test
+    public void testShouldNotChangeVariableNamesWhenTheyNamedAfterKeyword() {
+        Transformation t = new Transformation()
+                .variable("$width", 10)
+                .chain()
+                .width("$width + 10 + width");
+
+        assertEquals("$width_10/w_$width_add_10_add_w", t.generate());
+    }
 }