[css-text-3] Typo fix. (#3782)

Author: heycam

css-text-3/Overview.bs

@@ -1509,7 +1509,7 @@ Text Processing</h3>
     <div class=example>
       This example illustrates the consequence of [=hanging=] white space
       at the end of the line
-      on text alignement.
+      on text alignment.
       <pre><code class=lang-css>
       p {
         white-space: pre-wrap;