add sharp to dev dependencies

Author: sylvaindumont

.travis.yml

@@ -17,4 +17,3 @@ addons:
 osx_image: xcode8
 before_install:
   - if [[ "$TRAVIS_OS_NAME" == "linux" ]]; then export CXX=g++-4.8; fi
-  - npm install sharp@^0.19.0

package.json

@@ -16,6 +16,7 @@
   },
   "devDependencies": {
     "chai": "^3.5.0",
+    "sharp": "^0.19.0",
     "mocha": "^3.0.2"
   }
 }