Introduce yarn and upgrade package dependencies

.travis.yml

@@ -1,18 +1,10 @@
 language: node_js
 
 node_js:
-    - "5.7"
-    - "5.6"
-    - "5.5"
-    - "5.4"
-    - "5.3"
-    - "5.2"
-    - "5.1"
-    - "5.0"
-    - "4.2"
-    - "0.12"
-    - "0.11"
-    - "0.10"
+    - "7"
+    - "6"
+    - "5"
+    - "4"
 
 notifications:
     email:
@@ -22,7 +14,7 @@ notifications:
         on_failure: change
 
 before_script:
-    - npm install
+    - yarn install --pure-install
 
 script:
-    - npm test
+    - yarn run test

package.json

@@ -25,12 +25,12 @@
   },
   "homepage": "https://github.com/rezzza/gulp-uglifycss",
   "dependencies": {
-    "gulp-util": "~3.0.7",
-    "through2": "~2.0.1",
-    "uglifycss": "~0.0.20"
+    "gulp-util": "^3.0.8",
+    "through2": "^2.0.3",
+    "uglifycss": "^0.0.25"
   },
   "devDependencies": {
-    "mocha": "~2.4.5",
-    "should": "~8.2.2"
+    "mocha": "^3.2.0",
+    "should": "^11.2.1"
   }
 }