Update .gitignore file to include Carthage's artifacts (#1581)

* Update .gitignore file [Carthage]

* Add Cartfile.resolved file

Quoting from Carthage's README.md on Github:
"Along the way, Carthage will have created some build artifacts. The most important of these is the Cartfile.resolved file, which lists the versions that were actually built for each framework. Make sure to commit your Cartfile.resolved, because anyone else using the project will need that file to build the same framework versions."

.gitignore

@@ -32,3 +32,6 @@ playground.xcworkspace
 /.buckconfig.local
 /.buckd
 
+# Carthage
+Carthage/Checkouts
+Carthage/Build

Cartfile.resolved

@@ -0,0 +1,4 @@
+git "https://chromium.googlesource.com/webm/libwebp" "v0.6.0"
+github "pinterest/PINCache" "3.0.1-beta.7"
+github "pinterest/PINOperation" "1.1.2"
+github "pinterest/PINRemoteImage" "3.0.0-beta.14"