Bump solc from 0.6.8 to 0.6.9

Bumps [solc](https://github.com/ethereum/solc-js) from 0.6.8 to 0.6.9.
- [Release notes](https://github.com/ethereum/solc-js/releases)
- [Commits](ethereum/solc-js@v0.6.8...v0.6.9)

Signed-off-by: dependabot[bot] <support@github.com>

package.json

@@ -48,7 +48,7 @@
     "truffle-contract": "~4.0.31",
     "truffle-hdwallet-provider": "~1.0.17",
     "truffle-assertions": "^0.9.2",
-    "solc": "^0.6.8",
+    "solc": "^0.6.9",
     "solidity-docgen": "^0.5.3",
     "web3": "^1.2.8",
     "web3-provider-engine": "~15.0.12",