fix: enhancement of isExternal (#2093)

src/core/util/core.js

@@ -96,5 +96,8 @@ export function isExternal(url) {
   ) {
     return true;
   }
+  if (/^\/\\/.test(url)) {
+    return true;
+  }
   return false;
 }

test/unit/core-util.test.js

@@ -59,5 +59,17 @@ describe('core/util', () => {
 
       expect(result).toBeTruthy();
     });
+
+    test('external url with one \\', () => {
+      const result = isExternal('/\\example.github.io/docsify/demo.md');
+
+      expect(result).toBeTruthy();
+    });
+
+    test('external url with two \\', () => {
+      const result = isExternal('/\\\\example.github.io/docsify/demo.md');
+
+      expect(result).toBeTruthy();
+    });
   });
 });