Describe the bug
bats-gather-tests has a hard coded reference to lib and does not use $BATS_LIB when sourcing common.bash and others.

$ bats .
/usr/libexec/bats-core/bats-gather-tests: line 10: /usr/lib/bats-core/common.bash: No such file or directory

To Reproduce
Steps to reproduce the behavior:

1. Install bats-core to lib64
2. run bats . in a directory containing multiple bats files

Expected behavior
bats should run all tests

Environment (please complete the following information):

• Bats version [e.g. 1.4.0 or commit hash if applicable]: master
• operating system (including version): [e.g. Linux (please name your distribution!), FreeBSD, MacOS]: CentOS 7.9
• bash --version: [e.g. 5.1] 4.2.46
• Install method: [e.g. git submodule, distribution package manager, npm, homebrew, ...] bash install.sh /usr lib64

Cheers,
Peter