doc: magnum-integration may now depend on magnum-extras, swap the order.

This has a practical effect mainly on the Custom Buildsystems page,
where the dependency graph for Extras is now shown before Integration.

doc/Doxyfile

@@ -936,12 +936,12 @@ INPUT                  = ../src/Magnum \
                          ../../magnum-plugins/src/Magnum \
                          ../../magnum-plugins/src/MagnumPlugins \
                          ../../magnum-plugins/doc/ \
-                         ../../magnum-integration/src/Magnum \
-                         ../../magnum-integration/doc/ \
-                         ../../magnum-examples/doc/ \
                          ../../magnum-extras/src/Magnum \
                          ../../magnum-extras/src/Magnum/Ui/ui-gallery.cpp \
-                         ../../magnum-extras/doc/
+                         ../../magnum-extras/doc/ \
+                         ../../magnum-integration/src/Magnum \
+                         ../../magnum-integration/doc/ \
+                         ../../magnum-examples/doc/
 
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