tests: "grep -e" is not portable to all platforms

The "-e" option to grep is not needed unless specifying more than one
pattern, which we don't do.  Remove it to avoid restricting the tests on
platforms that do not have a grep that recognises "-e".

Signed-off-by: John Keeping <john@keeping.me.uk>
diff --git a/tests/t0108-patch.sh b/tests/t0108-patch.sh
index 6ee70b3..f15c893 100755
--- a/tests/t0108-patch.sh
+++ b/tests/t0108-patch.sh
@@ -9,19 +9,19 @@
 '
 
 run_test 'find `From:` line' '
-	grep -e "^From: " trash/tmp
+	grep "^From: " trash/tmp
 '
 
 run_test 'find `Date:` line' '
-	grep -e "^Date: " trash/tmp
+	grep "^Date: " trash/tmp
 '
 
 run_test 'find `Subject:` line' '
-	grep -e "^Subject: commit 5" trash/tmp
+	grep "^Subject: commit 5" trash/tmp
 '
 
 run_test 'find `cgit` signature' '
-	 tail -1 trash/tmp | grep -e "^cgit"
+	 tail -1 trash/tmp | grep "^cgit"
 '
 
 run_test 'find initial commit' '
@@ -33,7 +33,7 @@
 '
 
 run_test 'find `cgit` signature' '
-	tail -1 trash/tmp | grep -e "^cgit"
+	tail -1 trash/tmp | grep "^cgit"
 '
 
 tests_done