Conform to FilesAdapter Interface

[dplewis]

https://github.com/parse-community/parse-server/blob/master/src/Adapters/Files/FilesAdapter.js

[codecov]

Codecov Report

Merging #73 into master will not change coverage.
The diff coverage is 92.4%.

@@           Coverage Diff           @@
##           master      #73   +/-   ##
=======================================
  Coverage   94.23%   94.23%           
=======================================
  Files           2        2           
  Lines         156      156           
  Branches       33       33           
=======================================
  Hits          147      147           
  Misses          9        9

Impacted Files	Coverage Δ
index.js	93.02% <92.4%> (ø)	⬆️

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