Fix goreportcard issues (#271)

* Fixed misspell

* Fixed ineffassign

`user` and `password` always got overwritten
`orderedVals` was initialized with an empty array but always got overwritten by either `sortByLines()` or `sortAlphabetical`
`err` was assigned a `nil` value that was either overwritten or unused anyways

* Fix comment for DeletePath

The comment assumed the method was named Delete, i guess a rename happened at some point

* Update doc_test.go

doc_test.go

@@ -16,13 +16,14 @@ func Example_tree() {
 		fmt.Println("Error ", err.Error())
 	} else {
 		// retrieve data directly
-		user := config.Get("postgres.user").(string)
-		password := config.Get("postgres.password").(string)
+		directUser := config.Get("postgres.user").(string)
+		directPassword := config.Get("postgres.password").(string)
+		fmt.Println("User is", directUser, " and password is", directPassword)
 
 		// or using an intermediate object
 		configTree := config.Get("postgres").(*toml.Tree)
-		user = configTree.Get("user").(string)
-		password = configTree.Get("password").(string)
+		user := configTree.Get("user").(string)
+		password := configTree.Get("password").(string)
 		fmt.Println("User is", user, " and password is", password)
 
 		// show where elements are in the file