Update dependency dash to v1.15.0

Author: renovate-bot

requirements.txt

@@ -1,7 +1,7 @@
 Brotli==1.0.7
 click==7.1.2
 cssmin==0.2.0
-dash==1.14.0
+dash==1.15.0
 dash-core-components==1.10.2
 dash-html-components==1.0.3
 dash-renderer==1.6.0