Set version of ts to 1.5.0-beta

Author: Quramy

package.json

@@ -8,7 +8,7 @@
   },
   "repository": "https://github.com/Quramy/tsuquyomi.git",
   "devDependencies": {
-    "typescript": "1.5.0-alpha"
+    "typescript": "1.5.0-beta"
   },
   "scripts": {
     "test": "echo \"Error: no test specified\""