Lock in Solidity 0.6.8 on CircleCI (#27)

* Fix Makefile on macOS
* Lock circleci to solc:0.6.8-alpine
* Lock version to 0.6.8

Makefile

@@ -8,13 +8,14 @@ clean:
 	@rm -rf combined.json
 
 compile: clean
+	@# Note: using /bin/echo for macOS
 	@git submodule update --recursive --init
 	@solc --metadata-literal --bin --abi --combined-json=abi,bin,bin-runtime,srcmap,srcmap-runtime,ast,metadata,storage-layout --overwrite -o . deposit_contract.sol tests/deposit_contract.t.sol
-	@echo -n '{"abi": ' > deposit_contract.json
+	@/bin/echo -n '{"abi": ' > deposit_contract.json
 	@cat DepositContract.abi >> deposit_contract.json
-	@echo -n ', "bytecode": "0x' >> deposit_contract.json
+	@/bin/echo -n ', "bytecode": "0x' >> deposit_contract.json
 	@cat DepositContract.bin >> deposit_contract.json
-	@echo -n '"}' >> deposit_contract.json
+	@/bin/echo -n '"}' >> deposit_contract.json
 
 
 export DAPP_SKIP_BUILD:=1

circle.yml

@@ -3,15 +3,14 @@ version: 2.1
 jobs:
   build:
     docker:
-      - image: cimg/base:2020.01
+      - image: ethereum/solc:0.6.8-alpine
     steps:
       - checkout
       - run:
-          name: Install solidity
+          name: Install build essentials
           command: |
-            sudo add-apt-repository ppa:ethereum/ethereum
+            apk update
-            sudo apt-get update
+            apk add git make
-            sudo apt-get install solc
       - run:
           name: Compile the contract
           command: make

deposit_contract.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: Apache-2.0
 
-pragma solidity ^0.6.0;
+pragma solidity 0.6.8;
 
 // This interface is designed to be compatible with the Vyper version.
 interface IDepositContract {