Break out build osx before_install into script

Author: cthrax

.travis.yml

@@ -8,7 +8,7 @@ os:
   - osx
 script: npm run-script test
 before_install:
-  - if [[ $TRAVIS_OS_NAME == "osx" ]]; then echo "updating nvm for osx"; brew update; brew install nvm; mkdir ~/.nvm; export NVM_DIR=~/.nvm && source $(brew --prefix nvm)/nvm.sh; nvm alias default $NODE_VERSION; fi
+  - source build_scripts/osx-before_install.sh
   - nvm install $NODE_VERSION
   - npm config set spin false
 install:

build_scripts/osx-before_install.sh

@@ -0,0 +1,12 @@
+# no shebang as it expects to be run in the current shell, not standalone
+if [[ $TRAVIS_OS_NAME == "osx" ]]; then
+    # Recommended by travis guys to always brew update first
+    brew update
+    # Install NVM
+    brew install nvm
+    # Use -p just in case the folder already exists
+    mkdir -p ~/.nvm
+    # Make sure the NVM_DIR is set before sourcing nvm.sh
+    export NVM_DIR=~/.nvm && source $(brew --prefix nvm)/nvm.sh
+    nvm alias default $NODE_VERSION
+fi