Fixes proto code generator for repeated types

[juanpedromoreno]

This PR fixes list types as repeated (for custom types) in the generated proto files.

case class Foo(bar: List[CustomType])

Results as:

message Foo {
   repeated CustomType bar = 1;
}

[fedefernandez]

👍

[codecov-io]

Codecov Report

Merging #43 into master will not change coverage.
The diff coverage is 0%.

@@           Coverage Diff           @@
##           master      #43   +/-   ##
=======================================
  Coverage   10.75%   10.75%           
=======================================
  Files          20       20           
  Lines         279      279           
  Branches        0        1    +1     
=======================================
  Hits           30       30           
  Misses        249      249

Impacted Files	Coverage Δ
rpc/src/main/scala/proto/converters.scala	0% <0%> (ø)	⬆️

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