fix(tests): Fix Jest error reporting

Add configuration to babel transformation that allows Jest to report errors with the correct line

number.

lib/jestPreprocessor.js

@@ -4,7 +4,8 @@ const jestPreset = require('babel-preset-jest')
 module.exports = {
   process: function (src) {
     const transformCfg = {
-      presets: ['es2015', 'react', 'stage-0', jestPreset]
+      presets: ['es2015', 'react', 'stage-0', jestPreset],
+      retainLines: true
     }
     return babel.transform(src, transformCfg).code
   }