[Bug] OSX CI broken again

[klevzoff]

Describe the bug
Recent CI builds of develop fail to run all unit tests that link (directly or indirectly through geosx_core) to Trilinos, with the following log:

test 104
        Start 104: testXML
104: Test command: /Users/travis/build/GEOSX/GEOSX/build-darwin-clang-debug/tests/testXML "-i" "/Users/travis/build/GEOSX/GEOSX/src/coreComponents/unitTests/xmlTests/basic_input.xml"
104: Test timeout computed to be: 1500
104: dyld: Library not loaded: /usr/local/opt/gcc/lib/gcc/10/libgfortran.5.dylib
104:   Referenced from: /usr/local/GEOSX/GEOSX_TPL/trilinos/lib/libepetra.12.dylib
104:   Reason: image not found
104/133 Test #104: testXML ..............................................Child aborted***Exception:   0.03 sec

See for example:
https://travis-ci.com/github/GEOSX/GEOSX/jobs/504150685
https://travis-ci.com/github/GEOSX/GEOSX/jobs/504480047
https://travis-ci.com/github/GEOSX/GEOSX/jobs/504819676

There have been no changes to the OSX environment on our side, I think something has silently changed in homebrew again.

Obviously, this affects all current PRs as well. I'm going to disable unit testing in OSX in #1412 , this issue is a reminder to fix it later.

[klevzoff]

No longer reproduces on Travis