[#149] Fix gitlint regex to match our policy

In our policy we mark commits not having a PR/Issue yet with a `[#XX]`
reference to be replaced after PR creation.

Signed-off-by: Stanislav Bogatyrev <s.bogatyrev@yadro.com>

.gitlint

@@ -1,9 +1,10 @@
 [general]
 fail-without-commits=true
+regex-style-search=true
 contrib=CC1
 
 [title-match-regex]
-regex=^\[\#[0-9]+\]\s
+regex=^\[\#[0-9X]+\]\s
 
 [ignore-by-title]
 regex=^Release(.*)