message: bump qt dep to 5.3+
diff: @@ -24,7 +24,7 @@ These are the dependencies currently used by Bitcoin Unlimited. You can find ins
  | protobuf | [2.6.3](https://github.com/google/protobuf/releases) | | No | | |
  | Python (tests) | | [3.4](https://www.python.org/downloads) | | | |
  | qrencode | [3.4.4](https://fukuchi.org/works/qrencode) | | No | | |
  -| Qt | [5.7.1](https://download.qt.io/official_releases/qt/) | 5.0+ | No | | |
  +| Qt | [5.7.1](https://download.qt.io/official_releases/qt/) | 5.3+ | No | | |
  | XCB | | | | | [Yes](https://github.com/bitcoin/bitcoin/blob/master/depends/packages/qt.mk#L94) (Linux only) |
  | xkbcommon | | | | | [Yes](https://github.com/bitcoin/bitcoin/blob/master/depends/packages/qt.mk#L93) (Linux only) |
  | ZeroMQ | [4.2.3](https://github.com/zeromq/libzmq/releases) | | No | | |
  