Fix awk gensub call in author_line_count.sh script.

NOTRY=TRUE

Bug: None
Change-Id: I706cf0a57e17f765bf90ccaad245a2c5573d8e0c
Reviewed-on: https://webrtc-review.googlesource.com/29740
Reviewed-by: Patrik Höglund <phoglund@webrtc.org>
Commit-Queue: Niels Moller <nisse@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#21109}

rtc_tools/author_line_count.sh

@@ -16,7 +16,7 @@ git log "$@" --pretty=format:%ae --shortstat \
   | gawk '
 /^[^ ]/ {
   /* Some author "email addresses" have a trailing @svn-id, strip that out. */
-  author = gensub(/^([^@]*@[^@]*).*/, "\\1", "", $1);
+  author = gensub(/^([^@]*@[^@]*).*/, "\\1", "g", $1);
 }
 /^ .*insertion/ { total[author] += $1 }
 /^ .*deletion/ { total[author] -= $1 }