Use invariant culture for regression tests

[patricksadowski]

Closes #89

With this change I've got two changes in the test image repo:

jpg/metadata/dotnet/Reconyx HF2 Pro Covert.jpg.txt
@@ -37,7 +37,7 @@ TYPE: JPEG
-[Reconyx HyperFire 2 Makernote - 0x0030] Firmware Date = 24/08/2018
+[Reconyx HyperFire 2 Makernote - 0x0030] Firmware Date = 08/24/2018
tif/ImageTestSuite/metadata/dotnet/efb780f70a7d94fa98adfc98d2aa8d50.tif.txt
@@ -56,7 +56,7 @@ TYPE: TIFF
-[Exif SubIFD - 0x9206] Subject Distance = ∞ metres
+[Exif SubIFD - 0x9206] Subject Distance = Infinity metres

[drewnoakes]

Perfect, thanks!

FYI I've started migrating this tooling to the metadata-extractor-images repo (here https://github.com/drewnoakes/metadata-extractor-images/tree/source/src/dotnet). That way we can have the code alongside the data it creates, both for Java and .NET, and update both languages at the same time.