Update dependency dotenv to v3.1.5

Author: renovate[bot]

Gemfile.lock

@@ -16,7 +16,7 @@ GEM
     coderay (1.1.3)
     concurrent-ruby (1.2.3)
     diff-lcs (1.5.1)
-    dotenv (3.1.4)
+    dotenv (3.1.6)
     faraday (1.10.4)
       faraday-em_http (~> 1.0)
       faraday-em_synchrony (~> 1.0)