docs(typo): fix punctuation (#1817)

Author: jamiedishy

docs/guide/state.md

@@ -4,7 +4,7 @@
 
 <div class="scrimba"><a href="https://scrimba.com/p/pnyzgAP/cWw3Zhb" target="_blank" rel="noopener noreferrer">Try this lesson on Scrimba</a></div>
 
-Vuex uses a **single state tree** - that is, this single object contains all your application level state and serves as the "single source of truth". This also means usually you will have only one store for each application. A single state tree makes it straightforward to locate a specific piece of state, and allows us to easily take snapshots of the current app state for debugging purposes.
+Vuex uses a **single state tree** - that is, this single object contains all your application level state and serves as the "single source of truth." This also means usually you will have only one store for each application. A single state tree makes it straightforward to locate a specific piece of state, and allows us to easily take snapshots of the current app state for debugging purposes.
 
 The single state tree does not conflict with modularity - in later chapters we will discuss how to split your state and mutations into sub modules.