tests: fixed the vim mode line in a test file.

Author: agentzh

t/154-semaphore.t

@@ -1,4 +1,4 @@
-# vim:set ft=ts=4 sw=4 et fdm=marker:
+# vim:set ft= ts=4 sw=4 et fdm=marker:
 use lib 'lib';
 use Test::Nginx::Socket::Lua;