Investigate failing tests on Linux

[ole]

4 tests are currently failing on Linux:

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2019-10-29T00:29:17.9614291Z /__w/Ampere/Ampere/Tests/AmpereTests/UnitAreaTests.swift:18: error: UnitAreaTests.testDivisionWithDefaultUnits : XCTAssertTrue failed - "m" is not the same unit as "m"
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2019-10-29T00:29:17.9616731Z /__w/Ampere/Ampere/Tests/AmpereTests/UnitAreaTests.swift:10: error: UnitAreaTests.testMultiplicationWithDefaultUnits : XCTAssertTrue failed - "m²" is not the same unit as "m²"
...
2019-10-29T00:29:17.9618076Z /__w/Ampere/Ampere/Tests/AmpereTests/UnitAreaTests.swift:26: error: UnitAreaTests.testMultiplicationWithNonDefaultUnits : XCTAssertTrue failed - "m²" is not the same unit as "m²"
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2019-10-29T00:29:17.9666816Z /__w/Ampere/Ampere/Tests/AmpereTests/UnitVolumeTests.swift:19: error: UnitVolumeTests.testWithNonBaseUnits : XCTAssertEqual failed: ("0.0001 m³") is not equal to ("0.001 m³") - "0.0001 m³" is not equal to "100.0 cm³"
...

[ole]

Fixed 3 of these in a1b90fe. The other one is a bigger deal, I created #25 for it.