Update frontenddevelopers.rst

docs/building_your_site/frontenddevelopers.rst

@@ -205,7 +205,7 @@ Extra attributes can be specified with the syntax ``attribute="value"``:
 No validation is performed on attributes added in this way so it's possible to add `src`, `width`, `height` and `alt` of your own that might conflict with those generated by the tag itself.
 
 
-**Generating the image "as foo" to access individual properties **
+**Generating the image "as foo" to access individual properties**
 
 Wagtail can assign the image data to another variable using Django's ``as`` syntax: