docs: fix typo in page guide (vuepress#508)

Author: matej-marjanovic

docs/guide/page.md

@@ -17,7 +17,7 @@ Assuming this is the directory structure of your markdown files:
    └─ README.md
 ```
 
-Take the `docs` directory as your [sourceDir](../reference/cli.md), e.g. your are running `vuepress dev docs` command. Then the route paths of your markdown files would be:
+Take the `docs` directory as your [sourceDir](../reference/cli.md), e.g. you are running `vuepress dev docs` command. Then the route paths of your markdown files would be:
 
 |   Relative Path    |      Route Path      |
 |--------------------|----------------------|