fix: grammar mistakes

first/explain/comments/main.go

@@ -13,7 +13,7 @@ import "fmt"
 /*
 main function
 Go executes this program using this function.
-There should be only one main file in a main package.
+There should be only one main file in the main package.
 Executable programs are also called as "commands".
 */
 func main() {

first/explain/packages/what/main.go

@@ -17,7 +17,7 @@ func main() {
 
 	// Here, `main()` can access `bye()` and `hey()`
 
-	// It's because: bye.go, hey.go and main.go
+	// It's because bye.go, hey.go and main.go
 	//   are in the main package.
 
 	bye()