platform: etherscan: support ETHERSCAN_API_KEY environment variable

Fixes #567

Author: elopez

crytic_compile/platform/etherscan.py

@@ -310,6 +310,8 @@ def compile(self, crytic_compile: "CryticCompile", **kwargs: str) -> None:
         only_bytecode = kwargs.get("etherscan_only_bytecode", False)
 
         etherscan_api_key = kwargs.get("etherscan_api_key", None)
+        if etherscan_api_key is None:
+            etherscan_api_key = os.getenv("ETHERSCAN_API_KEY")
 
         export_dir = kwargs.get("export_dir", "crytic-export")
         export_dir = os.path.join(