tool: fix typo in -root-certs description

Without the space the help output is:

    Implies thatverification is required.

Change-Id: If7ff91ef70f2d968da5f8c76de562996c83dff2f
Reviewed-on: https://boringssl-review.googlesource.com/14246
Reviewed-by: David Benjamin <davidben@google.com>
Commit-Queue: David Benjamin <davidben@google.com>
CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>
diff --git a/tool/client.cc b/tool/client.cc
index 6cd40fb..6bc8e39 100644
--- a/tool/client.cc
+++ b/tool/client.cc
@@ -107,7 +107,7 @@
     },
     {
       "-root-certs", kOptionalArgument,
-      "A filename containing one of more PEM root certificates. Implies that"
+      "A filename containing one of more PEM root certificates. Implies that "
       "verification is required.",
     },
     {