Match README description for checkMD5

[jpumford]

This PR updates the code to follow the README.

I noticed the checkMD5 option was not available on the MongoMemoryServer class constructor, though the README indicated it is an option.

Here's a quick PR passing through the option to do an MD5 check for the downloaded mongo binary.

I also added two quick log statements in the MD5 check function. If that's a problem I can take them out, but they were useful to me and may be useful to someone else running in debug mode.

[codecov]

Codecov Report

Merging #342 into master will increase coverage by 0.06%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #342      +/-   ##
==========================================
+ Coverage   78.66%   78.73%   +0.06%     
==========================================
  Files           9        9              
  Lines         928      931       +3     
  Branches      265      266       +1     
==========================================
+ Hits          730      733       +3     
+ Misses        197      196       -1     
- Partials        1        2       +1     

Impacted Files	Coverage Δ
...mongodb-memory-server-core/src/util/MongoBinary.ts	77.10% <100.00%> (+0.27%)	⬆️
...memory-server-core/src/util/MongoBinaryDownload.ts	75.12% <100.00%> (+0.26%)	⬆️
...ongodb-memory-server-core/src/MongoMemoryServer.ts	92.07% <0.00%> (ø)

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[nodkz]

Thanks for your contribution!