labhub: Change regex pattern for 'invite_cmd'

The original file used regex with '\s*' responsible for matching 0 or
more whitespaces and led to matches like 'invite @userto developers' as
there are 0 backspaces between '@user' and 'to'. With '\s+' atleast 1
whitespace is required for the regex to match such commands. Added a
test to verify.

Fixes coala#512

plugins/labhub.py

@@ -72,7 +72,7 @@ def TEAMS(self, new):
         self._teams = new
 
     # Ignore LineLengthBear, PycodestyleBear
-    @re_botcmd(pattern=r'^(?:(?:welcome)|(?:inv)|(?:invite))\s+(?:(?:@?([\w-]+)(?:\s*(?:to)\s+(\w+))?)|(me))$',
+    @re_botcmd(pattern=r'^(?:(?:welcome)|(?:inv)|(?:invite))\s+(?:(?:@?([\w-]+)(?:\s+(?:to)\s+(\w+))?)|(me))$',
                re_cmd_name_help='invite ([@]<username> [to <team>]|me)')
     def invite_cmd(self, msg, match):
         """

tests/labhub_test.py

@@ -59,6 +59,8 @@ def test_invite_cmd(self):
         testbot.assertCommand('!invite meet to developers',
                                    ':poop:')
 
+        testbot.assertCommand('!invite meetto newcomers',
+                                   'Command "invite" / "invite meetto" not found.')
     def test_hello_world_callback(self):
         teams = {
             'coala newcomers': self.mock_team,