fix: same year as docs

Author: hartym

_includes/footer.html

@@ -1,7 +1,7 @@
 <footer class="footer">
     <div class="container">
         <p>
-            {{ site.title }} • 2017-{{ site.time | date: '%Y' }} • Apache License, Version 2.0
+            {{ site.title }} • 2015-{{ site.time | date: '%Y' }} • Apache License, Version 2.0
         </p>
         <br>
         <ul class="footer-links">