gl-renderer: Fix a typo in the output_set_border description

Signed-off-by: Jason Ekstrand <jason@jlekstrand.net>
diff --git a/src/gl-renderer.h b/src/gl-renderer.h
index db42f6c..bdfe93e 100644
--- a/src/gl-renderer.h
+++ b/src/gl-renderer.h
@@ -75,8 +75,8 @@
 	 * tightly packed.
 	 *
 	 * The top and bottom textures will extend over the sides to the
-	 * full width of the bordered window while.  The right and left
-	 * edges, however, will extend only to the top and bottom of the
+	 * full width of the bordered window.  The right and left edges,
+	 * however, will extend only to the top and bottom of the
 	 * compositor surface.  This is demonstrated by the picture below:
 	 *
 	 * +-----------------------+