Peg react-element-to-jsx-string version to exactly 2.5.0

bootstrap-tests.js relies on the particulars of this module's string formatting behavior, so let's be defensive here.

Author: motiz88

package.json

@@ -48,7 +48,7 @@
     "line-by-line": "^0.1.4",
     "mocha": "^2.4.5",
     "react-addons-test-utils": "^0.14.7",
-    "react-element-to-jsx-string": "^2.5.0",
+    "react-element-to-jsx-string": "=2.5.0",
     "replaceall": "^0.1.6",
     "webpack": "^2.1.0-beta.4",
     "webpack-dev-server": "^2.0.0-beta"