Use new eslint-plugin-functional instead of tslint-immutable

src/file/paragraph/math/radical/math-degree.ts

@@ -3,7 +3,7 @@ import { XmlComponent } from "@file/xml-components";
 import { MathComponent } from "../math-component";
 
 export class MathDegree extends XmlComponent {
-    public constructor(children?: MathComponent[]) {
+    public constructor(children?: readonly MathComponent[]) {
         super("m:deg");
 
         if (!!children) {

src/file/paragraph/math/radical/math-radical.ts

@@ -7,8 +7,8 @@ import { MathDegree } from "./math-degree";
 import { MathRadicalProperties } from "./math-radical-properties";
 
 export interface IMathRadicalOptions {
-    readonly children: MathComponent[];
-    readonly degree?: MathComponent[];
+    readonly children: readonly MathComponent[];
+    readonly degree?: readonly MathComponent[];
 }
 
 export class MathRadical extends XmlComponent {