build for scala 2.11

note the code changes I had to do to get scala 2.11 to compile.

This looks strange as it want's a warning in 2.10

The compiler error before the code change was:

```
[error] /home/diego/work/lift/modules/paypal/src/main/scala/net/liftmodules/paypal/Rules.scala:37: type mismatch;
[error]  found   : net.liftmodules.paypal.PaypalSSL.type
[error]  required: () => net.liftmodules.paypal.PaypalConnection
[error]     val connection = new FactoryMaker[() => PaypalConnection](() => PaypalSSL){}
[error]                                                                     ^
[error] /home/diego/work/lift/modules/paypal/src/main/scala/net/liftmodules/paypal/Rules.scala:41: type mismatch;
[error]  found   : String("/classpath/paypal/en_buynow_68x23.gif")
[error]  required: () => String
[error]     val button = new FactoryMaker[() => String](() => "/classpath/paypal/en_buynow_68x23.gif"){}
[error]                                                       ^
[error] two errors found
[error] (compile:compile) Compilation failed
[error] Total time: 5 s, completed Jun 7, 2014 12:55:47 AM

```

It would be great if anyone who uses the paypal module could try this branch to make sure the code change doesn't break your app.