404.md: expand contractions (#620)

Author: maxim-belkin

404.md

@@ -5,12 +5,12 @@ permalink: 404.html
 title: "Page not found"
 ---
 
-# Oops! We can't find that page.
+# Oops! We cannot find that page.
 {: style="text-align: center;"}
 
 > ## Our apologies!
 >
-> We can't seem to find the page you're looking for.
+> We cannot seem to find the page you are looking for.
 > Try going back to the <a href="javascript:history.back()">previous page</a> or
 > navigate to any other page using the navigation bar above
 > {%- if site.kind == "lesson" -%} or the schedule below {%- endif -%}.