Merge branch 'travis-ci-osx-fixes'

* travis-ci-osx-fixes:
  travis-ci/osx: switch to xcode 10.1, since 9.4 is not compatible with gcc-8
  travis-ci/osx: install gcc and fix CC

.travis.yml

@@ -3,6 +3,7 @@ os:
   - osx
 sudo: false
 dist: trusty
+osx_image: xcode10.1
 
 branches:
   except:
@@ -50,7 +51,7 @@ before_install:
   - export TIMEOUT=50
   - if [ "$TRAVIS_OS_NAME" == "osx" ]; then
       if [ "$CC" == "gcc" ]; then
-        export CC=$(ls -t /usr/local/bin/gcc-?.?);
+        export CC=$(ls /usr/local/Cellar/gcc/*/bin/gcc-?);
       fi
 
       export OPENSSL_ROOT=$(echo /usr/local/Cellar/openssl/*);
@@ -82,6 +83,7 @@ addons:
     - openssl
     - lcov
     - libtool
+    - gcc
 
 
 script: