Use print_r instead of echo

- use of `echo` and `print` is discouraged according to codacy

lib/Gocdb_Services/EmailService.php

@@ -34,14 +34,14 @@ private function getConfigSendEmail() {
     }
 
     private function mockMail($to, $subject, $message, $additionalHeaders = "", $additionalParameters = "") {
-        echo "<!--\n";
-        echo "Sending mail disabled, but would have sent:\n";
-        echo "$additionalHeaders\n";
-        echo "To: $to\n";
-        echo "Subject: $subject\n";
-        echo "\n$message\n";
-        echo "\nAdditional Parameters: $additionalParameters\n";
-        echo "-->\n";
+        print_r("<!--\n");
+        print_r( "Sending mail disabled, but would have sent:\n");
+        print_r( "$additionalHeaders\n");
+        print_r( "To: $to\n");
+        print_r( "Subject: $subject\n");
+        print_r( "\n$message\n");
+        print_r( "\nAdditional Parameters: $additionalParameters\n");
+        print_r( "-->\n");
         return True;
     }
 }