Make tests compile with text-2.1

Problem: tests do not compile when text-2.1 is used, because
there are is a conflict in module names.
`Data.Text.IO.Utf8` was added to `text` in version 2.1.
GHC reports ambiguous modules error.

Solution: specify the package explicitly using the PackageImports
extension.

Author: gromakovsky

test/Test/Utf8/ReadWrite.hs

@@ -5,6 +5,7 @@
 
 {-# LANGUAGE LambdaCase          #-}
 {-# LANGUAGE OverloadedStrings   #-}
+{-# LANGUAGE PackageImports      #-}
 {-# LANGUAGE ScopedTypeVariables #-}
 
 module Test.Utf8.ReadWrite where
@@ -22,7 +23,7 @@ import Hedgehog (Property, forAll, property, (===))
 import Test.HUnit (Assertion, assertFailure)
 
 import qualified Data.Text.IO as T
-import qualified Data.Text.IO.Utf8 as Utf8
+import qualified "with-utf8" Data.Text.IO.Utf8 as Utf8
 import qualified System.IO as IO
 import qualified System.IO.Utf8 as Utf8