Bug Fix Proto Code Generator for Custom Types

[juanpedromoreno]

Type.Arg within the input parameters are optional (Option[scala.meta.Type.Arg]). Hence, toString method was printing the file with the existential type. For example:

message CustomType2 {
   string foo = 1;
   Some(CustomType1) bar = 2;
}

This fix comes to solve it, making the output as follows:

message CustomType2 {
   string foo = 1;
   CustomType1 bar = 2;
}

[codecov-io]

Codecov Report

Merging #42 into master will decrease coverage by 0.07%.
The diff coverage is 0%.

@@            Coverage Diff             @@
##           master      #42      +/-   ##
==========================================
- Coverage   10.83%   10.75%   -0.08%     
==========================================
  Files          20       20              
  Lines         277      279       +2     
  Branches        1        0       -1     
==========================================
  Hits           30       30              
- Misses        247      249       +2

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

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