Update PHP versions and Travis setup

[whikloj]

GitHub Issue: Islandora/documentation#940

What does this Pull Request do?

Change the versions of PHP to test against and the Travis setup.

What's new?

• Does this change require documentation to be updated? no
• Does this change add any new dependencies? no
• Does this change require any other modifications to be made to the repository (ie. Regeneration activity, etc.)? no
• Could this change impact execution of existing code? no

How should this be tested?

Travis should pass.

Interested parties

@Islandora-CLAW/committers

[whikloj]

@dannylamb I think this will need to go in before your travis-badge one. If it passes.

[codecov]

Codecov Report

Merging #73 into master will decrease coverage by 0.31%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master      #73      +/-   ##
============================================
- Coverage     97.33%   97.01%   -0.32%     
  Complexity       12       12              
============================================
  Files             1        1              
  Lines            75       67       -8     
============================================
- Hits             73       65       -8     
  Misses            2        2

Impacted Files	Coverage Δ	Complexity Δ
src/FedoraApi.php	97.01% <0%> (-0.32%)	12% <0%> (ø)

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[dannylamb]

@whikloj Can you update this so we get the latest version of ml/JsonLD now that your PR has been merged?