Tests when ran outside of repo

[ThinkChaos]

Hi,

Thanks for the tool, I'm trying to use it to get coverage reports in my GH Actions.
I'm building the binary myself using Nix which builds it fine, and then runs the tests. The way it fetches the sources is not a full clone, but just a "download as zip".
This causes the tests to fail since getCoverallsSourceFileName ends up returning an absolute path:

--- FAIL: TestParseCoverage (0.01s)
    main_test.go:66:
                Error Trace:    main_test.go:66
                Error:          Not equal:
                                expected: "main.go"
                                actual  : "/build/source/main.go"

                                Diff:
                                --- Expected
                                +++ Actual
                                @@ -1 +1 @@
                                -main.go
                                +/build/source/main.go
                Test:           TestParseCoverage
--- FAIL: TestConvertCoverage (0.00s)
    main_test.go:102:
                Error Trace:    main_test.go:102
                Error:          Not equal:
                                expected: "TN:\nSF:main.go\nDA:6,1\nDA:7,1\nDA:8,1\nDA:9,0\nDA:10,2\nDA:11,2\nLF:6\nLH:5\nend_of_record\n"
                                actual  : "TN:\nSF:/build/source/main.go\nDA:6,1\nDA:7,1\nDA:8,1\nDA:9,0\nDA:10,2\nDA:11,2\nLF:6\nLH:5\nend_of_record\n"

                                Diff:
                                --- Expected
                                +++ Actual
                                @@ -1,3 +1,3 @@
                                 TN:
                                -SF:main.go
                                +SF:/build/source/main.go
                                 DA:6,1
                Test:           TestConvertCoverage
--- FAIL: TestPathResolverFunc (0.00s)
    main_test.go:110:
                Error Trace:    main_test.go:110
                Error:          Not equal:
                                expected: "main.go"
                                actual  : "/build/source/main.go"

                                Diff:
                                --- Expected
                                +++ Actual
                                @@ -1 +1 @@
                                -main.go
                                +/build/source/main.go
                Test:           TestPathResolverFunc
FAIL
FAIL    github.com/jandelgado/gcov2lcov 0.018s
FAIL

I can workaround this by skipping the tests run, but thought I'd report it here :)

[jandelgado]

For now, the easiest way to run the test would be to create an empty directory .git in the projects root dir, before the tests are run (i.e. mkdir .git). I'll check if we can get rid off the code checking for a vcs root dir....