Accept error messages like '+CME ERROR:58' without a space after ':'

My A6 GSM modem returns such error codes. This caused the library to
hang, waiting for a response indefinitely.  After this change modem
initialization succeeds and it's possible to send SMS messages etc.

It could be also the cause of #24, the symptoms are very similar.

Author: ppetr

gsmmodem/serial_comms.py

@@ -18,7 +18,7 @@ class SerialComms(object):
     # End-of-line read terminator
     RX_EOL_SEQ = '\r\n'
     # End-of-response terminator
-    RESPONSE_TERM = re.compile(r'^OK|ERROR|(\+CM[ES] ERROR: \d+)|(COMMAND NOT SUPPORT)$')
+    RESPONSE_TERM = re.compile(r'^OK|ERROR|(\+CM[ES] ERROR: ?\d+)|(COMMAND NOT SUPPORT)$')
     # Default timeout for serial port reads (in seconds)
     timeout = 1