fix: when install plugin in devDependencies cant use plugin (#70)

* chore: add test code

* chore: add test code

* chore: improve code coverage to 95%

* fix: when install p plugin in devDependencies cant use plugin

lib/core/loadPlugins.js

@@ -42,6 +42,12 @@ class Plugin {
     const ctx = this.ctx;
     const packagePath = pathFn.join(ctx.baseDir, 'package.json');
     const pluginDir = ctx.pluginDir;
+    const extend = function (target, source) {
+      for (var obj in source) {
+        target[obj] = source[obj];
+      }
+      return target;
+    };
 
     // Make sure package.json exists
     return fs.exists(packagePath).then(function (exist) {
@@ -50,7 +56,7 @@ class Plugin {
       // Read package.json and find dependencies
       return fs.readFile(packagePath).then(function (content) {
         const json = JSON.parse(content);
-        const deps = json.dependencies || json.devDependencies || {};
+        const deps = extend(json.dependencies || {}, json.devDependencies || {});
 
         return Object.keys(deps);
       });