Add test support for @RequestMapping(path = "/"). Fixes gh-387.

[calaroche]

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[codecov[bot]]

Codecov Report

Merging #409 into 2.2.x will increase coverage by 0.11%. The diff coverage is n/a.

@@             Coverage Diff              @@
##              2.2.x     #409      +/-   ##
============================================
+ Coverage     79.02%   79.13%   +0.11%     
- Complexity      444      445       +1     
============================================
  Files            59       59              
  Lines          1740     1740              
  Branches        244      244              
============================================
+ Hits           1375     1377       +2     
+ Misses          257      256       -1     
+ Partials        108      107       -1     

Impacted Files	Coverage Δ	Complexity Δ
...ork/cloud/openfeign/support/SpringMvcContract.java	87.63% <0.00%> (+1.07%)	55.00% <0.00%> (+1.00%)

[OlgaMaciaszek]

Thanks, @calaroche. Will review this tomorrow.