…alue

Technically brace patterns like `*.{js}` are invalid because braces should
always contain at least one comma or a sequence,
for example `*.{js,ts}` or `file{1..10}.js`.

The `micromatch` library used to match patterns to files will silently ignore
such invalid braces and thus lead to the pattern always matching zero files.
This is a unintuitive, so lint-staged should normalize such cases
by simply removing the unnecessary braces before matching files.