Don't assume a subscript for bare words if space before the [...] in a string

[snoopyjc]

Don't assume a subscript for bare words if space before the [...] in a string. For example:

"Usage: $prog [options] <file>"

Generates this code:

f"Usage: {prog[options]}] <file>"

instead of this code:

f"Usage: {prog} [options] <file>"

[snoopyjc]

Fixed in https://github.com/snoopyjc/pythonizer