Downgrade dotenv for Ruby 2.7 support

Author: andreibondarev

Gemfile

@@ -9,4 +9,4 @@ gem "rake", "~> 13.0"
 
 gem "rspec", "~> 3.0"
 gem "standard", "~> 1.28.0"
-gem "dotenv", "~> 3.1.4"
+gem "dotenv", "~> 2.8.1"

Gemfile.lock

@@ -9,7 +9,7 @@ GEM
   specs:
     ast (2.4.2)
     diff-lcs (1.5.0)
-    dotenv (3.1.4)
+    dotenv (2.8.1)
     faraday (2.7.10)
       faraday-net_http (>= 2.0, < 3.1)
       ruby2_keywords (>= 0.0.4)
@@ -75,7 +75,7 @@ PLATFORMS
 
 DEPENDENCIES
   cohere-ruby!
-  dotenv (~> 3.1.4)
+  dotenv (~> 2.8.1)
   rake (~> 13.0)
   rspec (~> 3.0)
   standard (~> 1.28.0)