doc/debugging_with_gdb: fix minor typo (space before comma)

R=golang-dev, r
CC=golang-dev
https://golang.org/cl/6610061

doc/debugging_with_gdb.html

@@ -36,8 +36,7 @@ debugged.
 
 <ul>
 <li>
-Show file and line number for code 
-, set breakpoints and disassemble:
+Show file and line number for code, set breakpoints and disassemble:
 <pre>(gdb) <b>list</b>
 (gdb) <b>list <i>line</i></b>
 (gdb) <b>list <i>file.go</i>:<i>line</i></b>