test: add case for --history-api-fallback

[snitin315]

• This is a bugfix
• This is a feature
• This is a code refactor
• This is a test update
• This is a docs update
• This is a metadata update

For Bugs and Features; did you add new tests?

yes

Motivation / Use-Case

add test case for --history-api-fallback

Breaking Changes

None

Additional Info

No

[codecov]

Codecov Report

Merging #3069 (e1efb8c) into master (e4fa1e7) will increase coverage by 1.66%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #3069      +/-   ##
==========================================
+ Coverage   90.64%   92.30%   +1.66%     
==========================================
  Files          37       37              
  Lines        1261     1261              
  Branches      328      328              
==========================================
+ Hits         1143     1164      +21     
+ Misses        110       92      -18     
+ Partials        8        5       -3     

Impacted Files	Coverage Δ
lib/utils/routes.js	98.21% <0.00%> (+3.57%)	⬆️
lib/utils/DevServerPlugin.js	100.00% <0.00%> (+26.02%)	⬆️

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[anshumanv]

Point of CLI tests when webpack-cli will be used to invoke dev server?