fix: Unable to submit an HTML file to JS3

[flacial]

Closes #62

Description

Students should be able to submit an HTML file for the 10th challenge. Currently, when they try to submit, they get:

✖ A valid challenge file could not be found. Make sure the file is not renamed and it has the following format: 1.js, 2.js, 3.js, ...etc

Fix

Add a condition to determine if the user is submitting for JS3 and whether the files have .js or .html extensions.

[codecov]

Codecov Report

Merging #63 (41e3655) into master (ca3de47) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master       #63   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           14        14           
  Lines          257       262    +5     
  Branches        35        37    +2     
=========================================
+ Hits           257       262    +5     

Impacted Files	Coverage Δ
src/messages.ts	100.00% <ø> (ø)
src/util/dynamicMessages.ts	100.00% <ø> (ø)
src/util/git.ts	100.00% <100.00%> (ø)
src/util/prompt.ts	100.00% <100.00%> (ø)

[flacial]

Students can't submit one JS and another HTML file to JS3. This will be fixed in a subsequent PR.