Fix typo in comments for JSON encoder and decoder (vapor#137)

* Fix typo in comments for JSON encoder and decoder

`mimmicks` -> `mimicks`

* Fix typo in PostgresJSONEncoder comment

Author: MaxDesiatov

Sources/PostgresNIO/Utilities/PostgresJSONDecoder.swift

@@ -1,6 +1,6 @@
 import Foundation
 
-/// A protocol that mimmicks the Foundation `JSONDecoder.decode(_:from:)` function.
+/// A protocol that mimicks the Foundation `JSONDecoder.decode(_:from:)` function.
 /// Conform a non-Foundation JSON decoder to this protocol if you want PostgresNIO to be
 /// able to use it when decoding JSON & JSONB values (see `PostgresNIO._defaultJSONDecoder`)
 public protocol PostgresJSONDecoder {

Sources/PostgresNIO/Utilities/PostgresJSONEncoder.swift

@@ -1,6 +1,6 @@
 import Foundation
 
-/// A protocol that mimmicks the Foundation `JSONEncoder.encode(_:)` function.
+/// A protocol that mimicks the Foundation `JSONEncoder.encode(_:)` function.
 /// Conform a non-Foundation JSON encoder to this protocol if you want PostgresNIO to be
 /// able to use it when encoding JSON & JSONB values (see `PostgresNIO._defaultJSONEncoder`)
 public protocol PostgresJSONEncoder {