fix: handle links with a _self target (#321)

Links having a `_self` target could be handled by Found.
This fix is based on a [PR](https://github.com/ReactTraining/react-router/pull/6138/files#diff-8c17f8f99262d24cba447ddc8f465455R41) in react-router.

src/BaseLink.js

@@ -33,15 +33,16 @@ class BaseLink extends React.Component {
 
     // Don't do anything if the user's onClick handler prevented default.
     // Otherwise, let the browser handle the link with the computed href if the
-    // event wasn't an unmodified left click, or if the link has a target.
+    // event wasn't an unmodified left click, or if the link has a target other
+    // than _self.
     if (
       event.defaultPrevented ||
       event.metaKey ||
       event.altKey ||
       event.ctrlKey ||
       event.shiftKey ||
       event.button !== 0 ||
-      target
+      (target && target !== '_self')
     ) {
       return;
     }

test/BaseLink.test.js

@@ -87,14 +87,23 @@ describe('<BaseLink>', () => {
       expect(router.push).not.toBeCalled();
     });
 
-    it('should not navigate if target is defined', () => {
+    it('should not navigate if target is defined and not _self', () => {
       const link = mount(
         <BaseLink to="/" match={{}} router={router} target="_blank" />,
       );
 
       link.find('a').simulate('click', { button: 0 });
       expect(router.push).not.toBeCalled();
     });
+
+    it('should navigate if target is _self', () => {
+      const link = mount(
+        <BaseLink to="/" match={{}} router={router} target="_self" />,
+      );
+
+      link.find('a').simulate('click', { button: 0 });
+      expect(router.push).toBeCalled();
+    });
   });
 
   describe('active state', () => {