fix(link): Use gatsby Link for CTA button

src/components/Header/components/Login.js

@@ -1,20 +1,23 @@
 import React from 'react';
 import PropTypes from 'prop-types';
 import { Button } from 'react-bootstrap';
+import { Link } from 'gatsby';
 
 import './login.css';
 
 function Login({ children, ...restProps }) {
   return (
-    <Button
-      {...restProps}
-      bsStyle='default'
-      className={(restProps.block ? 'btn-cta-big' : '') + ' signup-btn btn-cta'}
-      href='/signin'
-      target='_blank'
-      >
-      {children || 'Sign In'}
-    </Button>
+    <Link to='/signin'>
+      <Button
+        {...restProps}
+        bsStyle='default'
+        className={
+          (restProps.block ? 'btn-cta-big' : '') + ' signup-btn btn-cta'
+        }
+        >
+        {children || 'Sign In'}
+      </Button>
+    </Link>
   );
 }