y2m: Authenticate with GH to get better rate limiting.

otherwise we get "error listing repositories in github", because curl replies
{
  "message": "API rate limit exceeded for 999.999.999.999. (But here's the good news: Authenticated requests get a higher rate limit. Check out the documentation for more details.)",
  "documentation_url": "https://developer.github.com/v3/#rate-limiting"
}

y2m

@@ -204,6 +204,7 @@ get_repos_page() # {{{
   )
 
   curl --silent --verbose --show-error \
+    --netrc \
     --dump-header $headersfile \
     --output $responsefile \
     ${etag:+--header 'If-None-Match: '$etag} \