[css-text-3] Fix manual rendering in example

Author: frivoal

css-text-3/Overview.bs

@@ -3311,7 +3311,7 @@ Cursive Scripts</h4>
            For example, in the middle of
         this paragraph is an equation,
         which is centered:
-                         x + y = z
+                     x + y = z
         The first line after the equation
         is flush (else it would look like
         we started a new paragraph).