getKeyRecoveryParam method reusing variable e, type incorrect

[bradlhart]

@types/elliptic states that getKeyRecoveryParam e variable is Error | undefined: https://github.com/DefinitelyTyped/DefinitelyTyped/blob/a9f3af6e4416678bad8027c15627683621f532f1/types/elliptic/index.d.ts#L219

However, other than within the scope of the catch (e) {...} where it is Error | undefined, the type is more likely BNInput (or one of the types BNInput represents) as it is passed into recoverPubKey's msg argument: https://github.com/DefinitelyTyped/DefinitelyTyped/blob/a9f3af6e4416678bad8027c15627683621f532f1/types/elliptic/index.d.ts#L213

Likely why the @types/elliptic has the type wrong is due to e being redeclared in the catch statement. This PR is just to fix the redeclaration.

[coveralls]

Coverage remained the same at 88.928% when pulling 74b774f on bradlhart:master into e71b2d9 on indutny:master.

[irfan798]

I'm having the same issue with typescript, thank you for pointing that out @bradlhart