fix formatting error on bitmonero print_block return

Example of current return for `print_block 912345`:

    timestamp: 1452793716
    previous hash:
b61c58b2e0be53fad5ef9d9731a55e8a81d972b8d90ed07c04fd37ca6403ff78
    nonce: 1646
    is orphan: 0
    height: 912345
    depth: 85434
    hash:
e22cf75f39ae720e8b71b3d120a5ac03f0db50bba6379e2850975b4859190bc6difficul
ty: 815625611
    reward: 7388968946286
    {
      "major_version": 1,
      "minor_version": 2,
      …

Without `std::endl`, the difficulty gets smashed on the end of the hash.

src/daemon/rpc_command_executor.cpp

@@ -66,7 +66,7 @@ namespace {
       << "is orphan: " << header.orphan_status << std::endl
       << "height: " << boost::lexical_cast<std::string>(header.height) << std::endl
       << "depth: " << boost::lexical_cast<std::string>(header.depth) << std::endl
-      << "hash: " << header.hash
+      << "hash: " << header.hash << std::endl
       << "difficulty: " << boost::lexical_cast<std::string>(header.difficulty) << std::endl
       << "reward: " << boost::lexical_cast<std::string>(header.reward);
   }