Escape backslash in assemble module docs

library/files/assemble

@@ -74,7 +74,7 @@ options:
   regexp:
     description:
       - Assemble files only if C(regex) matches the filename. If not set,
-        all files are assembled. All "\" (backslash) must be escaped as
+        all files are assembled. All "\\" (backslash) must be escaped as
         "\\\\" to comply yaml syntax. Uses Python regular expressions; see
         U(http://docs.python.org/2/library/re.html).
     required: false