Properly get the commit range for cache

.travis.yml

@@ -14,8 +14,16 @@ install:
   - pod --version
 before_script:
   - pod install
+  - git diff --quiet "$TRAVIS_COMMIT_RANGE" -- ; GIT_DIFF_EXIT_CODE=$?
   - |
-    if [ ! $(git diff --name-only master..."$TRAVIS_COMMIT" | grep "Cartfile.resolved") ] && [ -d "Carthage/Build" ]; then
+    if [ "$GIT_DIFF_EXIT_CODE" -gt 1 ] ; then
+        git remote set-branches --add origin master
+        git fetch
+        TRAVIS_COMMIT_RANGE=origin/master...
+    fi
+  - echo $TRAVIS_COMMIT_RANGE
+  - |
+    if [ ! $(git diff --name-only "$TRAVIS_COMMIT_RANGE" | grep "Cartfile.resolved") ] && [ -d "Carthage/Build" ]; then
       echo "Use cached carthage dependencies."
       ls -ld Carthage/Build/iOS/*framework
     else
@@ -23,7 +31,7 @@ before_script:
       travis_wait 45 carthage bootstrap --platform iOS
     fi
   - |
-    if [ ! $(git diff --name-only master..."$TRAVIS_COMMIT" | grep -E "gopenpgp_build.sh|gopenpgpwrapper.go") ] && [ -d "go/dist/Gopenpgpwrapper.framework" ]; then
+    if [ ! $(git diff --name-only "$TRAVIS_COMMIT_RANGE" | grep -E "gopenpgp_build.sh|gopenpgpwrapper.go") ] && [ -d "go/dist/Gopenpgpwrapper.framework" ]; then
       echo "Use cached go dependencies."
       ls -ld go/dist/*framework
     else