Parse fail for Mapbox vector_tile.proto

[juselius]

Running Falanx on the Mapbox vector_tile.proto fails with:

Generating code for: vector_tile.proto
ERROR: proto file was not able to be parsed.

Error in Ln: 21 Col: 23
                optional string string_value = 1;
                      ^
Expecting: whitespace

I have spent some time trying to figure out what causes it, to no avail. The only way I can get falanx to process the file, is by removing all field specifications, leaving only the empty messages.

[gusty]

FYI: maybe it's better to open it here: https://github.com/fsprojects/falanx