Merge branch 'semantic/invalid-array-index' into 'master'

Add test case for illegal assignment in array index

See merge request !59

semantic/InvalidArrayIndex.invalid.mj

+class InvalidArrayIndex {
+
+    public void check(int x) {
+        int[] arr;
+        arr[5 = x] = x;
+    }
+
+    public static void main(String[] args) {
+    }
+
+}