Add namespace Typescript definition and fix test description

Author: Planeshifter

lib/node_modules/@stdlib/streams/node/debug-sink/docs/types/test.ts

@@ -53,7 +53,7 @@ function clbk( debug: Function, chunk: any, idx: number ) {
 	debugSinkStream( { 'objectMode': true }, clbk ); // $ExpectType Writable
 }
 
-// The constructor has an `objectMode` method returns a stream...
+// The constructor has an `objectMode` method which returns a stream...
 {
 	DebugSinkStream.objectMode(); // $ExpectType Writable
 	DebugSinkStream.objectMode( clbk ); // $ExpectType Writable

lib/node_modules/@stdlib/streams/node/debug/docs/types/test.ts

@@ -53,7 +53,7 @@ function clbk( debug: Function, chunk: any, idx: number ) {
 	debugStream( { 'objectMode': true }, clbk ); // $ExpectType Transform
 }
 
-// The constructor has an `objectMode` method returns a stream...
+// The constructor has an `objectMode` method which returns a stream...
 {
 	DebugStream.objectMode(); // $ExpectType Transform
 	DebugStream.objectMode( clbk ); // $ExpectType Transform