Fix @Args swapped with this.args (#40)

* Add failing test

* Resolve #35

Author: NullVoxPopuli

transforms/no-implicit-this/__testfixtures__/handlebars-with-positional-params.input.hbs

@@ -1,6 +1,7 @@
 {{my-component "string"}}
 {{my-component 1}}
 {{my-component foo}}
+{{my-component @foo}}
 {{my-component property}}
 {{my-component (my-helper property)}}
 {{my-component (my-helper "string")}}

transforms/no-implicit-this/__testfixtures__/handlebars-with-positional-params.output.hbs

@@ -1,6 +1,7 @@
 {{my-component "string"}}
 {{my-component 1}}
 {{my-component this.foo}}
+{{my-component @foo}}
 {{my-component this.property}}
 {{my-component (my-helper this.property)}}
 {{my-component (my-helper "string")}}

transforms/no-implicit-this/helpers/plugin.js

@@ -33,6 +33,8 @@ function transformPlugin(env, runtimeData, options = {}) {
     Program: paramTracker,
     ElementNode: paramTracker,
     PathExpression(ast) {
+      if (ast.data) return;
+
       let token = ast.parts[0];
 
       if (token !== 'this') {