Fix & update travis config

[garrettw]

• Removes ancient PHP versions
• Fixes broken tests
• Requires tests to pass on all PHP versions
• Fixes config to use correct PHPUnit version
• Moves code coverage uploader to the proper hook

Also, I see you are uploading code coverage data to Scrutinizer; however, code coverage is not enabled.
You'll need to add the following lines to the Scrutinizer config for this repo:

tools:
    external_code_coverage: true

... or I can add it in a .scrutinizer.yml file.