Allow digits in namespaces of type names

[JacekLach]

What happened?

types:
  conjure-imports:
    v1: v1.yml
  definitions:
    default-package: foo
    objects:
      Bar:
        fields:
          id: v1.BarId

results in an error:

java.lang.IllegalArgumentException: TypeNames must be a primitive type [any, string, integer, double, boolean, safelong, rid, bearertoken, uuid] or match pattern ^[A-Z][a-z0-9]+([A-Z][a-z0-9]+)*$: v1
        at com.google.common.base.Preconditions.checkArgument(Preconditions.java:455)
        at com.palantir.conjure.parser.types.names.TypeName.check(TypeName.java:46)
        at com.palantir.conjure.parser.types.names.ImmutableTypeName.validate(ImmutableTypeName.java:111)

What did you want to happen?

The namespace part of conjure imports is not externally visible and should not be subject to this regex.