make to_vec template parameters explicit

For some reason, Clang can infer <N,T> but GCC can't.
No big deal... we know exactly the ones we want anyway.

Change-Id: I15ba4d4edbd3bc0f37ebe3c2b6e411726cd9fb69
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/207341
Commit-Queue: Mike Klein <mtklein@google.com>
Reviewed-by: Michael Ludwig <michaelludwig@google.com>
1 file changed