Change encoding to UTF-8 for minimal.css

[jwakely]

CSS files should be UTF-8: https://www.w3.org/International/questions/qa-css-charset

[jwakely]

https://github.com/boostorg/filesystem/commit/9df2bfab58aadf35b4e01f2fd6252e1521409779#diff-36873c6a5a238ba4df45a47d97d80ead5ed664b3cb7e5a8fbe918020cc6889a4 replaced another ISO-8859-1 copyright symbol with (c), which would also be an option here. I just want to get rid of the ISO-8859-1 character in a file that doesn't specify its @charset, because it causes warnings for distro packagers.

[mclow]

I think changing to '(c)' is the simplest fix.

[jwakely]

OK thanks, I'll re-push with that change then...

[jwakely]

Now done consistently with https://github.com/boostorg/detail/commit/8c603a1894ec1d8abc7a0a538297923b0ac98b33

[jwakely]

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