Use isPromise module

This offers more robust checks and is unit tested separately.

Author: simonsmith

lib/index.js

@@ -8,6 +8,7 @@ const difference = require('lodash.difference');
 const encapsulationPlugins = require('./encapsulation');
 const fs = require('fs');
 const isEmpty = require('lodash.isempty');
+const isPromise = require('is-promise');
 const pify = require('pify');
 const postcssEasyImport = require('postcss-easy-import');
 const reporter = require('postcss-reporter');
@@ -178,10 +179,6 @@ function lintFile(css, options, filename) {
   return processor.process(css, options.postcss);
 }
 
-function isPromise(obj) {
-  return typeof obj.then === 'function';
-}
-
 function noop() {}
 
 function getFileContent(filename) {

package.json

@@ -17,6 +17,7 @@
     "commander": "~2.9.0",
     "cssnano": "^3.3.2",
     "fs-extra": "^2.1.2",
+    "is-promise": "^2.1.0",
     "lodash.difference": "^4.0.2",
     "lodash.isempty": "^4.1.1",
     "object-assign-deep": "0.0.4",

yarn.lock

@@ -2146,6 +2146,10 @@ is-primitive@^2.0.0:
   version "2.0.0"
   resolved "https://registry.yarnpkg.com/is-primitive/-/is-primitive-2.0.0.tgz#207bab91638499c07b2adf240a41a87210034575"
 
+is-promise@^2.1.0:
+  version "2.1.0"
+  resolved "https://registry.yarnpkg.com/is-promise/-/is-promise-2.1.0.tgz#79a2a9ece7f096e80f36d2b2f3bc16c1ff4bf3fa"
+
 is-property@^1.0.0:
   version "1.0.2"
   resolved "https://registry.yarnpkg.com/is-property/-/is-property-1.0.2.tgz#57fe1c4e48474edd65b09911f26b1cd4095dda84"