Add Cartfile.resolved for version pinning (#879)

.gitignore

@@ -22,7 +22,6 @@ xcuserdata
 *.pb.swift
 
 # Carthage built artifacts
-Cartfile.resolved
 Carthage
 
 # Generated debug symbols

Cartfile.resolved

@@ -0,0 +1 @@
+github "apple/swift-protobuf" "1.4.0"

build-carthage.sh

@@ -3,7 +3,7 @@
 set -euvx
 
 FRAMEWORK_NAME="${1:-MozillaAppServices.framework.zip}"
-carthage update --platform iOS swift-protobuf
+carthage update --platform iOS --cache-builds swift-protobuf
 ## When https://github.com/Carthage/Carthage/issues/2623 is fixed,
 ## carthage build --archive should work to produce a zip