docs: update license for 2021 (jina-ai#1625)

Author: cristianmtr

LICENSE

@@ -1,4 +1,4 @@
-Copyright 2020 Jina AI Limited.  All rights reserved.
+Copyright 2020-2021 Jina AI Limited.  All rights reserved.
 
 
                                  Apache License
@@ -178,7 +178,7 @@ Copyright 2020 Jina AI Limited.  All rights reserved.
 
    END OF TERMS AND CONDITIONS
 
-   Copyright 2020 Jina AI Limited
+   Copyright 2020-2021 Jina AI Limited
 
    Licensed under the Apache License, Version 2.0 (the "License");
    you may not use this file except in compliance with the License.