Added posthtml-css-modules for the test

Author: Ivan Demidov

package.json

@@ -46,6 +46,7 @@
     "nyc": "^6.4.4",
     "path-exists": "^3.0.0",
     "posthtml-bem": "^0.2.2",
+    "posthtml-css-modules": "^0.1.0",
     "posthtml-custom-elements": "^1.0.3",
     "read-pkg": "^1.1.0",
     "tempfile": "^1.1.1",