Fix broken link #1616

Job	Run time
Build Echidna on ubuntu-20.04	4m 2s
Build Echidna on ubuntu-20.04	4m 2s
Build Echidna on macos-latest	3m 20s
Build Echidna on macos-latest	3m 20s
Build Echidna on windows-latest	9m 5s
Build Echidna on windows-latest	9m 5s
Test with solc 0.4.25 on ubuntu-latest	4m 9s
Test with solc 0.4.25 on ubuntu-latest	4m 9s
Test with solc 0.5.7 on ubuntu-latest	5m 20s
Test with solc 0.5.7 on ubuntu-latest	5m 20s
Test with solc 0.6.12 on ubuntu-latest	4m 35s
Test with solc 0.6.12 on ubuntu-latest	6m 15s
Test with solc 0.7.5 on ubuntu-latest	5m 20s
Test with solc 0.7.5 on ubuntu-latest	5m 20s
Test with solc 0.4.25 on windows-latest	5m 30s
Test with solc 0.4.25 on windows-latest	5m 30s
Test with solc 0.5.7 on windows-latest	6m 55s
Test with solc 0.5.7 on windows-latest	6m 55s
Test with solc 0.6.12 on windows-latest	5m 32s
Test with solc 0.6.12 on windows-latest	5m 32s
Test with solc 0.7.5 on windows-latest	7m 14s
Test with solc 0.7.5 on windows-latest	7m 14s
	2h 3m 44s

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