Update "postinstall" to force a bash shell

[dorkian-gray]

"postinstall": "source ./scripts/source-me.sh && ./scripts/go-compile.sh ./vault-web-server" > "postinstall": "bash -c 'source ./scripts/source-me.sh && ./scripts/go-compile.sh ./vault-web-server'"

'source' command not recognised when running 'npm install' in Ubuntu 22.10; updating "postinstall" to use 'bash -c' instead of 'source', to force npm to use bash.

Apologies for any mistakes. Long time lurker, first time contributor.

[dorkian-gray]

Oops, missed the 'source' command in "start"