Error when default shell is non POSIX

When running the script with Fish and letting it modify the config.fish and bashrc files it will write the respective ```terminal-wakatime init``` at the bottom of the files. The problem is when I use a bash as a subshell (Ran from fish) that command outputs the config of fish rather than bash, and, since fish is not posix it doesn't works.

It can be corrected by always specifying which shell you're using, i.e; ```terminal-wakatime init bash```. But it should be made the default option for bash too (SInce it already specifies it when writing to config.fish).

Start at the `terminal-wakatime init` entry point and trace how the shell is selected when invoked from Fish versus Bash; the issue identifies `config.fish` and `bashrc` as the affected files. Done means the generated bashrc line explicitly requests Bash and a Bash subshell no longer receives Fish configuration.

Written by the indexing model from the issue text.