Fix GPS extraction for ImageMagick string format

[hyazinthh]

Updates the GPS coordinate regex to account for variations in whitespace.

On my system ImageMagick does not output any whitespace after the commas, making extraction fail with current regex:

$ identify -format "%[EXIF:GPSLatitude]\n" tests/files/mongolia.jpeg 
46/1,53903520/1000000,0/1

I assume this is version dependent but I haven't investigated any further.

$ identify --version
Version: ImageMagick 6.9.12-98 Q16 x86_64 18038 https://legacy.imagemagick.org
Copyright: (C) 1999 ImageMagick Studio LLC
License: https://imagemagick.org/script/license.php
Features: Cipher DPC Modules OpenMP(4.5) 
Delegates (built-in): bzlib djvu fftw fontconfig freetype heic jbig jng jp2 jpeg lcms lqr ltdl lzma openexr pangocairo png raw tiff webp wmf x xml zlib

[codecov]

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