workaround for "Malformed version number string" with CocoaPods

.travis.yml

@@ -3,63 +3,81 @@ podfile: ObjectiveCExample/Podfile
 xcode_workspace: ObjectiveCExample/ObjectiveCExample.xcworkspace
 matrix:
   include:
-    - osx_image: xcode9 # OS X 10.12
-      env: SDK="macosx"
-           DEVICE="OS X 10.12"
+    - osx_image: xcode9.4 # OS X 10.13
+      env: OSX_IMAGE="xcode9.4"
+           SDK="macosx"
+           DEVICE="OS X 10.13"
 
     - osx_image: xcode8.3 # OS X 10.12
-      env: SDK="macosx"
+      env: OSX_IMAGE="xcode8.3"
+           SDK="macosx"
            DEVICE="OS X 10.12"
 
     - osx_image: xcode7.3 # OS X 10.11
-      env: SDK="macosx"
+      env: OSX_IMAGE="xcode7.3"
+           SDK="macosx"
            DEVICE="OS X 10.11"
 
-    - osx_image: xcode9
-      env: SDK="appletvsimulator"
-           DEVICE="Apple TV 4K (11.0)" # oldest/newest for tvOS 11.x
+    - osx_image: xcode9.4
+      env: OSX_IMAGE="xcode9.4"
+           SDK="appletvsimulator"
+           DEVICE="Apple TV 4K (11.4)" # latest for tvOS 11.x
 
     - osx_image: xcode8.3
-      env: SDK="appletvsimulator"
+      env: OSX_IMAGE="xcode8.3"
+           SDK="appletvsimulator"
            DEVICE="Apple TV 1080p (10.2)" # latest for tvOS 10.x
 
     - osx_image: xcode8.3
-      env: SDK="appletvsimulator"
+      env: OSX_IMAGE="xcode8.3"
+           SDK="appletvsimulator"
            DEVICE="Apple TV 1080p (9.2)" # latest for tvOS 9.x
 
     - osx_image: xcode7.3
-      env: SDK="appletvsimulator"
+      env: OSX_IMAGE="xcode7.3"
+           SDK="appletvsimulator"
            DEVICE="Apple TV 1080p (9.0)" # oldest for tvOS 9.x
 
     - osx_image: xcode9
-      env: SDK="iphonesimulator"
+      env: OSX_IMAGE="xcode9"
+           SDK="iphonesimulator"
            DEVICE="iPhone X (11.0)" # oldest/newest for iOS 11.x
 
     - osx_image: xcode9
-      env: SDK="iphonesimulator"
+      env: OSX_IMAGE="xcode9"
+           SDK="iphonesimulator"
            DEVICE="iPhone 7 Plus (10.3.1)" # latest for iOS 10.x
 
     - osx_image: xcode8.3
-      env: SDK="iphonesimulator"
+      env: OSX_IMAGE="xcode8.3"
+           SDK="iphonesimulator"
            DEVICE="iPhone 5 (10.0)" # oldest for iOS 10.x
 
     - osx_image: xcode8.3
-      env: SDK="iphonesimulator"
+      env: OSX_IMAGE="xcode8.3"
+           SDK="iphonesimulator"
            DEVICE="iPhone 6s Plus (9.3)" # latest for iOS 9.x
 
     - osx_image: xcode7.3
-      env: SDK="iphonesimulator"
+      env: OSX_IMAGE="xcode7.3"
+           SDK="iphonesimulator"
            DEVICE="iPhone 4s (9.0)" # oldest for iOS 9.x
 
     - osx_image: xcode7.3
-      env: SDK="iphonesimulator"
+      env: OSX_IMAGE="xcode7.3"
+           SDK="iphonesimulator"
            DEVICE="iPhone 6 Plus (8.4)" # latest for iOS 8.x
 
     - osx_image: xcode7.3
-      env: SDK="iphonesimulator"
+      env: OSX_IMAGE="xcode7.3"
+           SDK="iphonesimulator"
            DEVICE="iPhone 4s (8.1)" # oldest for iOS 8.x
 
 before_install:
+  - if [ ${OSX_IMAGE} = "xcode7.3" ]; then
+        `Workaround for https://github.com/CocoaPods/CocoaPods/issues/7765`
+        gem install cocoapods -v '1.5.3';
+    fi
   - if [ ${SDK} = "macosx" ]; then
         SCHEME="ObjectiveCExample_macOS";
     elif [ ${SDK} = "appletvsimulator" ]; then