[Issue 21059] install.sh: posix_terminal returns false on Linux Mint 20

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=21059

--- Comment #1 from John Hall <john.michael.hall at gmail.com> ---
Comments on the forum from Bastiaan Veelo suggested that the issue is not
related to a specific version of Ubuntu, but may be due to how bash is (or is
not) called. 

This also is an issue for using docker. 
https://github.com/dlang/installer/commit/e084815001390538bbd6fe5be7c2d4d81ee681b7#commitcomment-40487617

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