refactor: use tuple for return type

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Author: anandkaranubc

lib/node_modules/@stdlib/math/base/special/cpolar/docs/types/index.d.ts

@@ -39,7 +39,7 @@ interface Cpolar {
 	* var v = cpolar( new Complex128( 5.0, 3.0 ) );
 	* // returns [ ~5.83, ~0.5404 ]
 	*/
-	( z: Complex128 ): Array<number>;
+	( z: Complex128 ): [ number, number ];
 
 	/**
 	* Computes the absolute value and the phase of a double-precision complex floating-point number and assigns results to a provided output array.

lib/node_modules/@stdlib/math/base/special/cpolar/docs/types/test.ts

@@ -24,7 +24,7 @@ import cpolar = require( './index' );
 
 // The function returns an array of numbers...
 {
-	cpolar( new Complex128( 5.0, 3.0 ) ); // $ExpectType number[]
+	cpolar( new Complex128( 5.0, 3.0 ) ); // $ExpectType [number, number]
 }
 
 // The compiler throws an error if the function is provided a complex number...