Test against go 1.19 too

Co-authored-by: Austin Sasko <austintyler0239@yahoo.com>

README.md

@@ -75,8 +75,8 @@ import _ "github.com/joho/godotenv/autoload"
 While `.env` in the project root is the default, you don't have to be constrained, both examples below are 100% legit
 
 ```go
-godotenv.Load("somerandomfile")
+_ = godotenv.Load("somerandomfile")
-godotenv.Load("filenumberone.env", "filenumbertwo.env")
+_ = godotenv.Load("filenumberone.env", "filenumbertwo.env")
 ```
 
 If you want to be really fancy with your env file you can do comments and exports (below is a valid env file)

fixtures/equals.env

@@ -1 +1,2 @@
 export OPTION_A='postgres://localhost:5432/database?sslmode=disable'
+