fix: add missing property

Author: kgryte

lib/node_modules/@stdlib/array/bool/docs/types/index.d.ts

@@ -360,6 +360,17 @@ declare class BooleanArray implements BooleanArrayInterface {
 	*/
 	at( i: number ): boolean | void;
 
+	/**
+	* Pointer to the underlying data buffer.
+	*
+	* @example
+	* var arr = new BooleanArray( 10 );
+	*
+	* var buf = arr.buffer;
+	* // returns <ArrayBuffer>
+	*/
+	readonly buffer: ArrayBuffer;
+
 	/**
 	* Length (in bytes) of the array.
 	*