Fix typos in travis script.

.travis.yml

@@ -125,10 +125,10 @@ before_install:
       # adding apt repos in travis is really fragile => retry a couple of times.
       for i in {1..10}; do travis_retry sudo apt-add-repository --yes 'ppa:ubuntu-toolchain-r/test' && break; sleep 2; done
       for i in {1..10}; do travis_retry sudo apt-get update && travis_retry sudo apt-get install --yes gcc-8  $(if [ -z "${BACKEND##*cpp*}" ]; then echo -n "g++-8"; fi ) && break; sleep 2; done
-      sudo update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-8 60 $(if [ -z "${BACKEND##*cpp*" ]; then echo " --slave /usr/bin/g++ g++ /usr/bin/g++-8"; fi)
+      sudo update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-8 60 $(if [ -z "${BACKEND##*cpp*}" ]; then echo " --slave /usr/bin/g++ g++ /usr/bin/g++-8"; fi)
       sudo update-alternatives --set gcc /usr/bin/gcc-8
       export CC=gcc
-      if [ -z "${BACKEND##*cpp*" ]; then sudo update-alternatives --set g++ /usr/bin/g++-8; export CXX=g++; fi
+      if [ -z "${BACKEND##*cpp*}" ]; then sudo update-alternatives --set g++ /usr/bin/g++-8; export CXX=g++; fi
     fi
 
   - |