Fix underscores in interface names

[drwpow]

When using nested objects, it wouldn’t transform underscores properly. Given:

properties: {
  remote_ids: {
    type: 'object', properties: { id: { type: 'string' } } },
  },
},

it would return the following interface:

interface UserRemote_ids {} // 🚫

This now returns the following, as expected:

interface UserRemoteIds {} // ✅

[codecov]

Codecov Report

Merging #29 into master will increase coverage by 2.19%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master      #29      +/-   ##
==========================================
+ Coverage   95.65%   97.84%   +2.19%     
==========================================
  Files           2        2              
  Lines          92       93       +1     
  Branches       34       34              
==========================================
+ Hits           88       91       +3     
+ Misses          4        2       -2

Impacted Files	Coverage Δ
src/swagger-2.ts	97.7% <100%> (+2.35%)	⬆️

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