Merge pull request firebase#536 from danielemaddaluno/patch-1

FacebookAppID must not have the prefix fb

Author: morganchen12

samples/swift/FirebaseUI-demo-swift/Info.plist

@@ -54,7 +54,7 @@
 <key>CFBundleVersion</key>
 <string>1</string>
 <key>FacebookAppID</key>
-<string>fb{your-app-id}</string>
+<string>{your-app-id}</string>
 <key>FacebookDisplayName</key>
 <string>{your-app-name}</string>
 <key>LSApplicationQueriesSchemes</key>