[package] fix version dependency

Resolves #365

Author: pkra

package.json

@@ -25,7 +25,7 @@
   "dependencies": {
     "is-fullwidth-code-point": "^2.0.0",
     "jsdom": "7.0 - 9.12",
-    "mathjax": "*"
+    "mathjax": "^2.7.2"
   },
   "scripts": {
     "test": "tape test/*.js"