Problem: some comments contain typos

src/mtrie.cpp

@@ -91,7 +91,7 @@ bool zmq::mtrie_t::add_helper (unsigned char *prefix_, size_t size_,
     if (c < min || c >= min + count) {
 
         //  The character is out of range of currently handled
-        //  charcters. We have to extend the table.
+        //  characters. We have to extend the table.
         if (!count) {
             min = c;
             count = 1;