ABC: add missing chain_context arg to VirtualMachineAPI's constructor.

This silences `mypy` error:

    eth/chains/base.py:250: error: Unexpected keyword argument "chain_context" for "VirtualMachineAPI"
    eth/abc.py:2270: note: "VirtualMachineAPI" defined here

This change has been copy-pasted from the previous PR.
I would've cherry-picked it in, but since then the constructor
has changed, adding in `consensus_context`, too.

Anyway, here's the previous PR's commit:

97cc8db

Author: veox

eth/abc.py

@@ -2481,6 +2481,7 @@ class VirtualMachineAPI(ConfigurableAPI):
     def __init__(self,
                  header: BlockHeaderAPI,
                  chaindb: ChainDatabaseAPI,
+                 chain_context: ChainContextAPI,
                  consensus_context: ConsensusContextAPI) -> None:
         """
         Initialize the virtual machine.