Revert "move to Debug for iOS builds"

We should stay on Release mode for performance reasons. We
can look into providing symbols for builds for crash log
purposes.

This reverts commit cf1ecb6976.

.travis.yml

@@ -38,7 +38,7 @@ matrix:
       env: BUILDTYPE=Debug JOBS=8 MASON_PLATFORM=osx
       compiler: clang
     - os: osx
-      env: BUILDTYPE=Debug JOBS=8 MASON_PLATFORM=ios
+      env: BUILDTYPE=Release JOBS=8 MASON_PLATFORM=ios
       compiler: clang
 
 env: