Update snappy version to 1.1.7.3

[lbergelson]

• updating snappy version 1.1.4 -> 1.1.7.3
• it might fix https://github.com/broadinstitute/picard/issues/1238

[codecov-io]

Codecov Report

Merging #1435 into master will increase coverage by 0.015%. The diff coverage is n/a.

@@               Coverage Diff               @@
##              master     #1435       +/-   ##
===============================================
+ Coverage     68.352%   68.367%   +0.015%     
- Complexity      8493      8495        +2     
===============================================
  Files            583       583               
  Lines          34410     34410               
  Branches        5729      5729               
===============================================
+ Hits           23520     23525        +5     
+ Misses          8669      8666        -3     
+ Partials        2221      2219        -2

Impacted Files	Coverage Δ	Complexity Δ
src/main/java/htsjdk/samtools/BAMFileReader.java	68.466% <0%> (+0.852%)	52% <0%> (+1%)	:arrow_up:
...htsjdk/samtools/util/nio/DeleteOnExitPathHook.java	90.476% <0%> (+9.524%)	4% <0%> (+1%)	:arrow_up: