fix(index): return types don't support promise rejection values

See jsdoc/jsdoc#1197

API.md

@@ -5,7 +5,7 @@
 
 * [UnRTF](#UnRTF)
     * [new UnRTF([binPath])](#new_UnRTF_new)
-    * [.convert(file, [options])](#UnRTF+convert) ⇒ <code>Promise.&lt;(string\|Error)&gt;</code>
+    * [.convert(file, [options])](#UnRTF+convert) ⇒ <code>Promise.&lt;string&gt;</code>
 
 <a name="new_UnRTF_new"></a>
 
@@ -17,13 +17,13 @@
 
 <a name="UnRTF+convert"></a>
 
-### unRTF.convert(file, [options]) ⇒ <code>Promise.&lt;(string\|Error)&gt;</code>
+### unRTF.convert(file, [options]) ⇒ <code>Promise.&lt;string&gt;</code>
 Converts an RTF file to HTML/LaTeX/RTF/TXT.
 Defaults to HTML output if no `output*` options are provided.
 UnRTF will use the directory of the original file to store embedded pictures.
 
 **Kind**: instance method of [<code>UnRTF</code>](#UnRTF)  
-**Returns**: <code>Promise.&lt;(string\|Error)&gt;</code> - Promise of stdout string on resolve, or Error object on rejection.  
+**Returns**: <code>Promise.&lt;string&gt;</code> - A promise that resolves with a stdout string, or rejects with an `Error` object.  
 **Author**: Frazer Smith  
 
 | Param | Type | Description |

src/index.js

@@ -110,7 +110,7 @@ class UnRTF {
 	 * @param {boolean=} options.outputWpml - Generate WPML output (UnRTF v0.19.4 or earlier only).
 	 * @param {boolean=} options.printVersionInfo - Print copyright and version info.
 	 * @param {boolean=} options.quiet - Do not print any leading comments in output (UnRTF v0.21.3 or later only).
-	 * @returns {Promise<string|Error>} Promise of stdout string on resolve, or Error object on rejection.
+	 * @returns {Promise<string>}  A promise that resolves with a stdout string, or rejects with an `Error` object.
 	 */
 	async convert(file, options = {}) {
 		const acceptedOptions = {

types/index.d.ts

@@ -25,10 +25,7 @@ export class UnRTF {
 	 * @param {boolean=} options.outputWpml - Generate WPML output (UnRTF v0.19.4 or earlier only).
 	 * @param {boolean=} options.printVersionInfo - Print copyright and version info.
 	 * @param {boolean=} options.quiet - Do not print any leading comments in output (UnRTF v0.21.3 or later only).
-	 * @returns {Promise<string|Error>} Promise of stdout string on resolve, or Error object on rejection.
+	 * @returns {Promise<string>}  A promise that resolves with a stdout string, or rejects with an `Error` object.
 	 */
-	convert(
-		file: string,
-		options?: object | undefined
-	): Promise<string | Error>;
+	convert(file: string, options?: object | undefined): Promise<string>;
 }