macOS CI: fix package conflicts due to Homebrew's Python 2

.circleci/config.yml

@@ -178,7 +178,10 @@ jobs:
       - *restore_cache
       - run:
           name: Install Homebrew dependencies
-          command: brew update && brew install ccache fftw cmake pkg-config libogg libvorbis lame libsndfile libsamplerate jack sdl libgig libsoundio stk fluid-synth portaudio fltk qt5 carla
+          command: |
+            # unlink Homebrew's python 2 to prevent an node-gyp error
+            brew unlink python@2 || true
+            brew update && brew install ccache fftw cmake pkg-config libogg libvorbis lame libsndfile libsamplerate jack sdl libgig libsoundio stk fluid-synth portaudio fltk qt5 carla
       - run:
           name: Install nodejs dependencies
           command: npm install -g appdmg

.travis/osx..before_install.sh

@@ -3,3 +3,5 @@
 set -e
 
 brew update
+# Python 2 may cause conflicts on dependency installation
+brew unlink python@2 || true