Switch Travis CI tests to using macOS 10.13 by default about mac-dev-playbook HOT 2 CLOSED

$ sudo easy_install pip
Searching for pip
Reading https://pypi.python.org/simple/pip/
Download error on https://pypi.python.org/simple/pip/: [SSL: TLSV1_ALERT_PROTOCOL_VERSION] tlsv1 alert protocol version (_ssl.c:590) -- Some packages may not be found!
Couldn't find index page for 'pip' (maybe misspelled?)
Scanning index of all packages (this may take a while)
Reading https://pypi.python.org/simple/
Download error on https://pypi.python.org/simple/: [SSL: TLSV1_ALERT_PROTOCOL_VERSION] tlsv1 alert protocol version (_ssl.c:590) -- Some packages may not be found!
No local packages or download links found for pip
error: Could not find suitable distribution for Requirement.parse('pip')
The command "sudo easy_install pip" failed and exited with 1 during .
Your build has been stopped.
/Users/travis/.travis/job_stages: line 166: shell_session_update: command not found