Fix vasturiano#516. Fix d3force types

Author: vasturiano

src/packages/react-force-graph-2d/index.d.ts

@@ -135,7 +135,7 @@ export interface ForceGraphMethods<
 
   // Force engine (d3-force) configuration
   d3Force(forceName: 'link' | 'charge' | 'center' | string): ForceFn<NodeObject<NodeType>> | undefined;
-  d3Force(forceName: 'link' | 'charge' | 'center' | string, forceFn: ForceFn<NodeObject<NodeType>>): ForceGraphKapsuleInstance;
+  d3Force(forceName: 'link' | 'charge' | 'center' | string, forceFn: ForceFn<NodeObject<NodeType>> | null): ForceGraphKapsuleInstance;
   d3ReheatSimulation(): ForceGraphKapsuleInstance;
 
   // Render control

src/packages/react-force-graph-3d/index.d.ts

@@ -141,7 +141,7 @@ export interface ForceGraphMethods<
 
   // Force engine (d3-force) configuration
   d3Force(forceName: 'link' | 'charge' | 'center' | string): ForceFn<NodeObject<NodeType>> | undefined;
-  d3Force(forceName: 'link' | 'charge' | 'center' | string, forceFn: ForceFn<NodeObject<NodeType>>): ForceGraphKapsuleInstance;
+  d3Force(forceName: 'link' | 'charge' | 'center' | string, forceFn: ForceFn<NodeObject<NodeType>> | null): ForceGraphKapsuleInstance;
   d3ReheatSimulation(): ForceGraphKapsuleInstance;
 
   // Render control

src/packages/react-force-graph-ar/index.d.ts

@@ -128,7 +128,7 @@ export interface ForceGraphMethods<
 
   // Force engine (d3-force) configuration
   d3Force(forceName: 'link' | 'charge' | 'center' | string): ForceFn<NodeObject<NodeType>> | undefined;
-  d3Force(forceName: 'link' | 'charge' | 'center' | string, forceFn: ForceFn<NodeObject<NodeType>>): ForceGraphKapsuleInstance;
+  d3Force(forceName: 'link' | 'charge' | 'center' | string, forceFn: ForceFn<NodeObject<NodeType>> | null): ForceGraphKapsuleInstance;
   d3ReheatSimulation(): ForceGraphKapsuleInstance;
 
   // Render control

src/packages/react-force-graph-vr/index.d.ts

@@ -132,7 +132,7 @@ export interface ForceGraphMethods<
 
   // Force engine (d3-force) configuration
   d3Force(forceName: 'link' | 'charge' | 'center' | string): ForceFn<NodeObject<NodeType>> | undefined;
-  d3Force(forceName: 'link' | 'charge' | 'center' | string, forceFn: ForceFn<NodeObject<NodeType>>): ForceGraphKapsuleInstance;
+  d3Force(forceName: 'link' | 'charge' | 'center' | string, forceFn: ForceFn<NodeObject<NodeType>> | null): ForceGraphKapsuleInstance;
   d3ReheatSimulation(): ForceGraphKapsuleInstance;
 
   // Render control