Fix compiler warnings in Travis builds

[freeekanayaka]

No description provided.

[codecov-io]

Codecov Report

Merging #90 into master will increase coverage by 0.7%.
The diff coverage is 54.23%.

@@           Coverage Diff            @@
##           master     #90     +/-   ##
========================================
+ Coverage      85%   85.7%   +0.7%     
========================================
  Files          48      46      -2     
  Lines        6881    6645    -236     
  Branches     1861    1798     -63     
========================================
- Hits         5849    5695    -154     
+ Misses       1032     950     -82

Impacted Files	Coverage Δ
src/election.c	92.03% <ø> (+0.58%)	⬆️
src/client.c	81.08% <ø> (+0.16%)	⬆️
src/recv_append_entries_result.c	89.65% <ø> (-0.35%)	⬇️
src/progress.c	88.8% <ø> (ø)	⬆️
src/uv_send.c	92.66% <ø> (+0.35%)	⬆️
src/recv_install_snapshot.c	44.18% <ø> (+1.96%)	⬆️
src/recv_request_vote_result.c	90.47% <ø> (+3.51%)	⬆️
src/tick.c	88.23% <ø> (+0.73%)	⬆️
src/recv_append_entries.c	88% <ø> (-0.24%)	⬇️
src/uv_recv.c	80.35% <ø> (ø)	⬆️
... and 31 more

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