[#219] Make sure we don't bother writing files that don't need updating

[somewhatabstract]

Summary
Turns out, when there are no broken edges, we were still opening and writing files when -u is specified. That's bad. So, we fixed it.

Issues
#219

Details
Also fixed a couple of typos in docs and code.

[codecov]

Codecov Report

Merging #262 into master will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master      #262   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           23        23           
  Lines          403       404    +1     
  Branches        68        68           
=========================================
+ Hits           403       404    +1     

Impacted Files	Coverage Δ
src/get-markers-from-files.js	100.00% <ø> (ø)
src/validate-and-fix.js	100.00% <100.00%> (ø)

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