Fix rst error detected by twine / PyPi.
Fix rst error detected by twine / PyPi.

Signed-off-by: Daniel Lim Wee Soong <d80bfdebad5865226377797a803502f9935337f3@gmail.com>
Signed-off-by: Tim 'mithro' Ansell <f857bf86f3aed4a1021a5247bd2399c65b7ad5cd@google.com>

SymbiFlow/sphinxcontrib-hdl-diagrams