test: Add trailing newline to error messages

The newline was removed from say_color in commit 222926ab to allow
printing test status in the beginning of the line. Error messages are
never followed by other text so we add the newline to error function.

test/test-lib.sh

@@ -144,7 +144,7 @@ else
 fi
 
 error () {
-	say_color error "error: $*"
+	say_color error "error: $*\n"
 	GIT_EXIT_OK=t
 	exit 1
 }