Don't run travis CI when modifying appveyor.yml

[rei2hu]

For #207.

So the issue was that the commit range was turning into FETCH_HEAD...master. The behaviour for running git diff with two endpoints separated by ... is specified here. The important part is that it deals with differences up to the second endpoint, in this case master, which means there were no file changes. You can see this in travis where there is an empty line.

I think the original PR for fb should have had $TRAVIS_BRANCH..FETCH_HEAD or $TRAVIS_BRANCH...FETCH_HEAD instead of FETCH_HEAD...$TRAVIS_BRANCH which makes almost no sense because a pr will almost always be ahead of the target branch.

Also, the modification to the TRAVIS_COMMIT_RANGE environment variable was unnecessary once travis-ci/travis-core#383 was merged.

[codecov-io]

Codecov Report

Merging #231 into master will decrease coverage by 37.87%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##           master     #231       +/-   ##
===========================================
- Coverage   69.55%   31.67%   -37.88%     
===========================================
  Files          11       11               
  Lines        3350     3002      -348     
  Branches     1981     1870      -111     
===========================================
- Hits         2330      951     -1379     
- Misses        393      461       +68     
- Partials      627     1590      +963

Impacted Files	Coverage Δ
src/parser.rs	25.99% <0%> (-50.23%)	⬇️
src/output.rs	9.55% <0%> (-48.53%)	⬇️
src/filter.rs	45.45% <0%> (-47.73%)	⬇️
src/producer.rs	38.22% <0%> (-47.57%)	⬇️
src/lib.rs	35.44% <0%> (-29.54%)	⬇️
src/main.rs	15.68% <0%> (-27.06%)	⬇️
src/path_rewriting.rs	32.2% <0%> (-26.45%)	⬇️
src/gcov.rs	32.6% <0%> (-16.38%)	⬇️

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[marco-c]

Looks good to me!