Use "travis_retry" script to see if it improves the build reliability.

.travis.yml

@@ -114,8 +114,8 @@ before_install:
   - |
     if [[ "$TRAVIS_OS_NAME" == "linux" ]]; then
       # adding apt repos in travis is really fragile => retry a couple of times.
-      for i in {1..10}; do sudo apt-add-repository --yes 'ppa:ubuntu-toolchain-r/test' && break; sleep 2; done
-      for i in {1..10}; do sudo apt-get update && sudo apt-get install --yes gcc-8  $(if [ "$BACKEND" = cpp ]; then echo -n "g++-8"; fi ) && break; sleep 2; done
+      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  $(if [ "$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 $(if [ "$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
@@ -125,7 +125,7 @@ before_install:
   - |
     if [[ "$TRAVIS_OS_NAME" == "osx" ]] || [[ "$STACKLESS" == "true" ]]; then # Install Miniconda
       if [[ "$TRAVIS_OS_NAME" == "osx" ]]; then CONDA_PLATFORM=MacOSX; else CONDA_PLATFORM=Linux; fi
-      curl -s -o miniconda.sh https://repo.continuum.io/miniconda/Miniconda$PY-latest-${CONDA_PLATFORM}-x86_64.sh
+      travis_retry curl -s -o miniconda.sh https://repo.continuum.io/miniconda/Miniconda$PY-latest-${CONDA_PLATFORM}-x86_64.sh
       bash miniconda.sh -b -p $HOME/miniconda && rm miniconda.sh
       #conda install --quiet --yes nomkl --file=test-requirements.txt --file=test-requirements-cpython.txt
       if [[ "$TRAVIS_OS_NAME" == "osx" ]]; then
@@ -139,7 +139,7 @@ before_install:
 
   - if [[ "$STACKLESS" == "true" ]]; then
       conda config --add channels stackless;
-      conda install --quiet --yes stackless;
+      travis_retry conda install --quiet --yes stackless;
     fi
 
 install: