fix: fix typing in theme overriding

[dr-itz]

This: { [K in keyof typeof HighlightSubject]?: string }

• gives a type with UPPER CASE keys, but the default theme and how it's resolved via TOKEN_TYPE_TO_HIGHLIGHT expects the values, i.e. lower case
• string is wrong type as a StyleFunction is expected and then called

I.e. the types suggest this
new SqlHighlighter({ RESERVED: 'red' }) but this has no effect. To get it to work w/o this fix:
new SqlHighlighter({ reserved: c.red.bold } as any)

[coveralls]

Pull Request Test Coverage Report for Build 15862431405

Details

• 7 of 7 (100.0%) changed or added relevant lines in 2 files are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage decreased (-0.7%) to 94.118%

---

Files with Coverage Reduction	New Missed Lines	%
src/SqlHighlighter.ts	1	93.18%

Totals
Change from base Build 6624426979:	-0.7%
Covered Lines:	152
Relevant Lines:	157

---

💛 - Coveralls

[B4nan]

thanks!