tools: fix broken format string

The format specifier is incomplete and without this the program will
fail at runtime, with "incomplete format" error.

PR-URL: https://github.com/nodejs/node/pull/7620
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>

tools/icu/shrink-icu-src.py

@@ -33,7 +33,7 @@ if os.path.isdir(options.icusmall):
     shutil.rmtree(options.icusmall)
 
 if not os.path.isdir(options.icusrc):
-    print 'Missing source ICU dir --icusrc=%' % (options.icusrc)
+    print 'Missing source ICU dir --icusrc=%s' % (options.icusrc)
     sys.exit(1)