Added fs-extra as a direct dependency of Blendid

The fs-extra is required directly by Blendid in file
`gulpfile.js/tasks/replace-files.js`. However, this dependency was expected
to be present transitively via `browser-sync`.

Since it's a direct dependency of Blendid, it should be listed as such in
the `package.json`. By not being present, it was causing us problem when
using Yarn workspaces where `fs-extra` was not resolvable correctly (
because it was in different `node_modules` folder).

Author: maoueh

package.json

@@ -33,6 +33,7 @@
     "del": "2.2.2",
     "es6-promise": "^4.1.1",
     "fancy-log": "^1.3.2",
+    "fs-extra": "^5.0.0",
     "gulp": "3.9.1",
     "gulp-autoprefixer": "3.1.1",
     "gulp-changed": "^2.0.0",

yarn.lock

@@ -2359,6 +2359,14 @@ fs-extra@3.0.1:
     jsonfile "^3.0.0"
     universalify "^0.1.0"
 
+fs-extra@^5.0.0:
+  version "5.0.0"
+  resolved "https://registry.yarnpkg.com/fs-extra/-/fs-extra-5.0.0.tgz#414d0110cdd06705734d055652c5411260c31abd"
+  dependencies:
+    graceful-fs "^4.1.2"
+    jsonfile "^4.0.0"
+    universalify "^0.1.0"
+
 fs.realpath@^1.0.0:
   version "1.0.0"
   resolved "https://registry.npmjs.org/fs.realpath/-/fs.realpath-1.0.0.tgz#1504ad2523158caa40db4a2787cb01411994ea4f"
@@ -3473,6 +3481,12 @@ jsonfile@^3.0.0:
   optionalDependencies:
     graceful-fs "^4.1.6"
 
+jsonfile@^4.0.0:
+  version "4.0.0"
+  resolved "https://registry.yarnpkg.com/jsonfile/-/jsonfile-4.0.0.tgz#8771aae0799b64076b76640fca058f9c10e33ecb"
+  optionalDependencies:
+    graceful-fs "^4.1.6"
+
 jsonfile@~1.1.0:
   version "1.1.1"
   resolved "https://registry.npmjs.org/jsonfile/-/jsonfile-1.1.1.tgz#da4fd6ad77f1a255203ea63c7bc32dc31ef64433"