Bump CITATION.cff version

Author: Tom94

CITATION.cff

@@ -20,5 +20,5 @@ keywords:
   - 'neural network, tiny, tensor cores, cuda'
 license: BSD-3-Clause
 license-url: https://github.com/NVlabs/tiny-cuda-nn/blob/master/LICENSE.txt
-version: 1.6
+version: 1.7
 date-released: '2021-04-21'