Simplify validation function.

Author: jelbourn

tools/release/prompt/new-version-prompt.ts

@@ -39,7 +39,7 @@ export async function promptForNewVersion(currentVersion: Version): Promise<Vers
     name: 'manualCustomVersion',
     message: 'Please provide a custom release name:',
     validate: enteredVersion =>
-      !parseVersionName(enteredVersion) ? 'This is not a valid Semver version' : true,
+      !!parseVersionName(enteredVersion) || 'This is not a valid Semver version',
     when: ({versionName}) => versionName === 'custom-release'
   }]);