Add type test for extended RouteOptions

[kibertoad]

Add type test to make sure that our way of augmenting route options is compatible with both route definition ways.

[codecov-io]

Codecov Report

Merging #15 (7f29c9e) into master (255b1d4) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##            master       #15   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            1         1           
  Lines           34        37    +3     
=========================================
+ Hits            34        37    +3     

Impacted Files	Coverage Δ
plugin.js	100.00% <0.00%> (ø)

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