fix: fix compatibility with verbatimModuleSyntax TS config option

[achou11]

Currently trying to build a library that imports types from this module and emits its own declarations. However, running TS on it fails when the verbatimModuleSyntax option is enabled on my project:

node_modules/rpc-reflector/lib/types.ts:1:10 - error TS1484: 'ErrorObject' is a type and must be imported using a type-only import when 'verbatimModuleSyntax' is enabled.

1 import { ErrorObject } from 'serialize-error'
           ~~~~~~~~~~~


Found 1 error in node_modules/rpc-reflector/lib/types.ts:1

There doesn't seem to be any downside to convert the import in question to an explicit type-only import, which I believe is generally recommended when possible anyways when working with TypeScript.

I didn't update the other imports in this file since that first one was the only one that caused the error. Open to fixing the other imports in this PR if it makes sense to.

[coveralls]

Pull Request Test Coverage Report for Build 10220698815

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 93.405%

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Totals
Change from base Build 6233270959:	0.0%
Covered Lines:	328
Relevant Lines:	342

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💛 - Coveralls

[coveralls]

Pull Request Test Coverage Report for Build 10188337538

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 93.405%

---

Totals
Change from base Build 6233270959:	0.0%
Covered Lines:	328
Relevant Lines:	342

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💛 - Coveralls

[EvanHahn]

Always a fan of using import type when possible.