Fix typo (en)

stomar · stomar · commit 3cac2f50c138 · 2019-03-04T15:48:38.000+01:00
diff --git a/en/documentation/index.md b/en/documentation/index.md
@@ -4,7 +4,7 @@ title: "Documentation"
 lang: en
 ---
 
-Guides, tutorials and reference material to help you learn more about Ruby
+Guides, tutorials, and reference material to help you learn more about Ruby
 {: .summary}
 
 ### Installing Ruby
