remove useless exclude declaration in MANIFEST.in (#16)

examples/update.sh is not included by the  recursive-include rule above.
This results in the following warning when building a source
distribution:
warning: no previously-included files found matching 'examples/update.sh

MANIFEST.in

@@ -7,5 +7,3 @@ include tests/VLGothic/*
 recursive-include examples blockdiagrc *.diag *.png *.svg
 recursive-include src *.py
 recursive-include tests README *.py *.diag *.gif *.png
-
-exclude examples/update.sh