fix API types

Author: nichoth

src/browser/index.ts

@@ -184,7 +184,7 @@ function formatArgs ({ diff, color, namespace, useColors }:{
     return args
 }
 
-function createDebug (namespace?:string|boolean):Debugger {
+function createDebug (namespace:string|boolean):Debugger {
     if (namespace === false) return noop
     const prevTime = Number(new Date())
     const color = selectColor(

src/cloudflare/index.ts

@@ -146,7 +146,7 @@ function formatArgs ({ diff, namespace }:{
     return args
 }
 
-function createDebug (namespace?:string, env?:Record<string, string>):Debugger;
+function createDebug (namespace:string, env?:Record<string, string>):Debugger;
 function createDebug (enabled:boolean):Debugger;
 function createDebug (
     namespaceOrEnabled?:string|boolean,

src/node/index.ts

@@ -150,7 +150,7 @@ let randomNamespace:string = ''
  * @return {Function}
  */
 export function createDebug (
-    namespace?:string|boolean|null,
+    namespace:string|boolean|null,
     env?:Record<string, any>
 ):Debugger {
     // eslint-disable-next-line