Fixes some bugs relatated to commands output handling

This seems to fix some of the bugs reported by issues like #114 and #190.

Seems that the standard library's os/exec package has some black magic to
detect if a writer is an actual *os.File, and some stuff are handled
differently, then.

Fixes #114
Fixes #190

task.go

@@ -248,8 +248,18 @@ func (e *Executor) runCommand(ctx context.Context, t *taskfile.Task, call taskfi
 
 		stdOut := e.Output.WrapWriter(e.Stdout, t.Prefix)
 		stdErr := e.Output.WrapWriter(e.Stderr, t.Prefix)
-		defer stdOut.Close()
-		defer stdErr.Close()
+		defer func() {
+			if _, ok := stdOut.(*os.File); !ok {
+				if closer, ok := stdOut.(io.Closer); ok {
+					closer.Close()
+				}
+			}
+			if _, ok := stdErr.(*os.File); !ok {
+				if closer, ok := stdErr.(io.Closer); ok {
+					closer.Close()
+				}
+			}
+		}()
 
 		err := execext.RunCommand(ctx, &execext.RunCommandOptions{
 			Command: cmd.Cmd,