configure.ac: fix cairo-glesv2 help text

Finally figured out why --enable-cairo-gles2 wasn't working like
configure --help said it should.
diff --git a/configure.ac b/configure.ac
index 550bb3c..a2bb537 100644
--- a/configure.ac
+++ b/configure.ac
@@ -96,7 +96,7 @@
   PKG_CHECK_MODULES(WAYLAND_COMPOSITOR, [wayland-client wayland-egl])
 fi
 
-AC_ARG_WITH(cairo-glesv2, AS_HELP_STRING([--with-cairo-gles2],
+AC_ARG_WITH(cairo-glesv2, AS_HELP_STRING([--with-cairo-glesv2],
               [Use GLESv2 cairo instead of full GL]),
               [cairo_modules="cairo-glesv2"],
               [cairo_modules="cairo-gl"])