test_that: fix typo in usage string.

BUG=None
TEST=test_that --help shows no typo.

Change-Id: I78c1b3619095842c38a4abeb39c4acb95850dbed
Reviewed-on: https://chromium-review.googlesource.com/195500
Commit-Queue: Jorge Lucangeli Obes <jorgelo@chromium.org>
Tested-by: Jorge Lucangeli Obes <jorgelo@chromium.org>
Reviewed-by: Aviv Keshet <akeshet@chromium.org>
diff --git a/site_utils/test_that.py b/site_utils/test_that.py
index fb6dd62..3c957be 100755
--- a/site_utils/test_that.py
+++ b/site_utils/test_that.py
@@ -495,7 +495,7 @@
                              'NAME-matching regular expression. Use '
                              'f:[FILE_PATTERN] to specify a filename matching '
                              'regular expression. Specified regular '
-                             'expressiosn will be implicitly wrapped in '
+                             'expressions will be implicitly wrapped in '
                              '^ and $.')
     default_board = cros_build_lib.GetDefaultBoard()
     parser.add_argument('-b', '--board', metavar='BOARD', default=default_board,