add some leading comment/directive tests

Author: aminya

spec/spec.js

@@ -114,6 +114,19 @@ pluginTester({
         commentTriggers: ['@babel', '@flow', '* @babel', '* @flow'],
       },
     },
+    {
+      code: `
+      "use babel";
+      "use strict";
+      `,
+      output: `
+      "use babel";
+      `,
+      pluginOptions: {
+        directiveTriggers: ['use babel'],
+        commentTriggers: ['@babel', '@flow', '* @babel', '* @flow'],
+      },
+    },
     {
       code: `
       "use strict";
@@ -159,5 +172,41 @@ pluginTester({
         commentTriggers: ['@babel', '@flow', '* @babel', '* @flow'],
       },
     },
+    {
+      code: `
+      // @flow
+      "use strict";
+      `,
+      output: ``,
+      pluginOptions: {
+        directiveTriggers: ['use babel'],
+        commentTriggers: ['@babel', '@flow', '* @babel', '* @flow'],
+      },
+    },
+    {
+      code: `
+      // @babel
+      // @flow
+      "use strict";
+      `,
+      output: ``,
+      pluginOptions: {
+        directiveTriggers: ['use babel'],
+        commentTriggers: ['@babel', '@flow', '* @babel', '* @flow'],
+      },
+    },
+    {
+      code: `
+      // @babel
+      "use strict";
+      // @flow
+      `,
+      output: `
+      `,
+      pluginOptions: {
+        directiveTriggers: ['use babel'],
+        commentTriggers: ['@babel', '@flow', '* @babel', '* @flow'],
+      },
+    },
   ]
 })