type fixes & docs

src/common/input/UnicodeV6.ts

@@ -84,7 +84,7 @@ function bisearch(ucs: number, data: number[][]): boolean {
 }
 
 export class UnicodeV6 implements IUnicodeVersionProvider {
-  public version = '6';
+  public readonly version = '6';
 
   constructor() {
     // init lookup table once

src/common/services/Services.ts

@@ -328,6 +328,6 @@ export interface IUnicodeService {
 }
 
 export interface IUnicodeVersionProvider {
-  version: string;
+  readonly version: string;
   wcwidth(ucs: number): 0 | 1 | 2;
 }