Update en_US.csv

Use US English spelling for "Optimization".

Author: davidangel

app/code/Magento/Cms/i18n/en_US.csv

@@ -133,7 +133,7 @@ Block,Block
 "Enable Page","Enable Page"
 Content,Content
 "Content Heading","Content Heading"
-"Search Engine Optimisation","Search Engine Optimisation"
+"Search Engine Optimization","Search Engine Optimization"
 "Meta Title","Meta Title"
 "Meta Keywords","Meta Keywords"
 "Meta Description","Meta Description"