Merge pull request #42 from alanjames1987/master

Fixes a typo.

Author: yyx990803

source/guide/index.md

@@ -53,7 +53,7 @@ Vue instances proxy all properties on data objects they observe. So once an obje
 
 The data objects are mutated in place, so modifying it by reference has the same effects as modifying `vm.$data`. This makes it possible for multiple Vue instances to observe the same piece of data. In larger applications it is also recommended to treat Vue instances as pure views, and externalize the data manipulation logic into a more discrete store layer.
 
-One caveat here is that once the observation has been initiated, Vue.js will not be able detect newly added or deleted properties. To get around that, observed objects are augmented with `$add` and `$delete` methods.
+One caveat here is that once the observation has been initiated, Vue.js will not be able to detect newly added or deleted properties. To get around that, observed objects are augmented with `$add` and `$delete` methods.
 
 ### Directives