Update BigNumber dep to ~9.0.0

[fabioberger]

Description

Supercedes: #2331

Updates our tooling's BigNumber dep to ~9.0.0.

Testing instructions

Types of changes

Checklist:

• Prefix PR title with [WIP] if necessary.
• Add tests to cover changes as needed.
• Update documentation as needed.
• Add new entries to the relevant CHANGELOG.jsons.

[buildsize]

File name	Previous Size	New Size	Change
init.py	60.47 KB	60.47 KB	0 bytes (0%)
abi_gen_dummy.ts	112.85 KB	[deleted]
lib_dummy.ts	7.04 KB	[deleted]
test_lib_dummy.ts	12.09 KB	[deleted]
environment.pickle	1.61 MB	1.61 MB	0 bytes (0%)
index.doctree	184.8 KB	184.8 KB	0 bytes (0%)
.buildinfo	230 bytes	230 bytes	0 bytes (0%)
genindex.html	5.6 KB	5.6 KB	0 bytes (0%)
index.html	2.52 KB	2.52 KB	0 bytes (0%)
objects.inv	375 bytes	375 bytes	0 bytes (0%)
py-modindex.html	3.07 KB	3.07 KB	0 bytes (0%)
search.html	2.84 KB	2.84 KB	0 bytes (0%)
searchindex.js	6.28 KB	6.28 KB	0 bytes (0%)
index.rst.txt	415 bytes	415 bytes	0 bytes (0%)
alabaster.css	10.92 KB	10.92 KB	0 bytes (0%)
basic.css	11.89 KB	11.89 KB	0 bytes (0%)
custom.css	42 bytes	42 bytes	0 bytes (0%)
doctools.js	9.05 KB	9.05 KB	0 bytes (0%)
documentation_options.js	303 bytes	303 bytes	0 bytes (0%)
file.png	286 bytes	286 bytes	0 bytes (0%)
jquery-[version].js	273.79 KB	273.79 KB	0 bytes (0%)
jquery.js	86.08 KB	86.08 KB	0 bytes (0%)
language_data.js	10.59 KB	10.59 KB	0 bytes (0%)
minus.png	90 bytes	90 bytes	0 bytes (0%)
plus.png	90 bytes	90 bytes	0 bytes (0%)
pygments.css	4.69 KB	4.69 KB	0 bytes (0%)
searchtools.js	15.61 KB	15.61 KB	0 bytes (0%)
underscore-[version].js	34.34 KB	34.34 KB	0 bytes (0%)
underscore.js	11.86 KB	11.86 KB	0 bytes (0%)
contract_addresses.html	16.8 KB	16.8 KB	0 bytes (0%)
contract_artifacts.html	8.24 KB	8.24 KB	0 bytes (0%)
json_schemas.html	12.55 KB	12.55 KB	0 bytes (0%)
order_utils.html	46.85 KB	46.85 KB	0 bytes (0%)
erc20_token.html	93.31 KB	93.31 KB	0 bytes (0%)
exchange.html	678.51 KB	678.51 KB	0 bytes (0%)
tx_params.html	9.41 KB	9.41 KB	0 bytes (0%)
local_message_signer.html	15.07 KB	15.07 KB	0 bytes (0%)
asset_data_utils.html	22.65 KB	22.65 KB	0 bytes (0%)
default_api.html	113.16 KB	113.16 KB	0 bytes (0%)
asset_proxy_owner.html	350.44 KB	350.44 KB	0 bytes (0%)
coordinator.html	133.77 KB	133.77 KB	0 bytes (0%)
coordinator_registry.html	39.72 KB	39.72 KB	0 bytes (0%)
dutch_auction.html	59.6 KB	59.6 KB	0 bytes (0%)
erc20_proxy.html	111 KB	111 KB	0 bytes (0%)
erc721_proxy.html	111.12 KB	111.12 KB	0 bytes (0%)
erc721_token.html	148.29 KB	148.29 KB	0 bytes (0%)
forwarder.html	110.46 KB	110.46 KB	0 bytes (0%)
i_asset_proxy.html	39.32 KB	39.32 KB	0 bytes (0%)
i_validator.html	30.37 KB	30.37 KB	0 bytes (0%)
i_wallet.html	27.63 KB	27.63 KB	0 bytes (0%)
multi_asset_proxy.html	148.59 KB	148.59 KB	0 bytes (0%)
order_validator.html	120.52 KB	120.52 KB	0 bytes (0%)
weth9.html	133.98 KB	133.98 KB	0 bytes (0%)
zrx_token.html	111.93 KB	111.93 KB	0 bytes (0%)
dev_utils.html	580.48 KB	580.48 KB	0 bytes (0%)
types.html	8.68 KB	8.68 KB	0 bytes (0%)
erc1155_mintable.html	288.23 KB	288.23 KB	0 bytes (0%)
erc1155_proxy.html	129.7 KB	129.7 KB	0 bytes (0%)
static_call_proxy.html	39.44 KB	39.44 KB	0 bytes (0%)

[coveralls]

Coverage remained the same at 75.743% when pulling cf8fd71 on update/bigNumberDep into 30f0168 on development.