Fix calcul of token.size for backticks

lib/rules_inline/backticks.js

@@ -32,7 +32,7 @@ module.exports = function backtick(state, silent) {
                                  .replace(/[ \n]+/g, ' ')
                                  .trim();
         token.position = start;
-        token.size = (matchStart + 1) - token.position;
+        token.size = matchEnd - token.position;
       }
       state.pos = matchEnd;
       return true;