Update services, tests, examples and composer packages

[mixisLv]

Updated:

• php version
• composer packages
• FedEx Rate Service v28 -> 31
• FedEx Track Service v19 -> v20
• FedEx Ship Service v26 -> v28
• FedEx Upload Document Service v11 -> v19
• FedEx Pickup Service v22 -> v23
• FedEx Open Ship Service v15 -> v20
• FedEx Validation and Commitment Service v14 -> v17

Fixed:

• travis
• tests
• examples

[mixisLv]

Hey @JeremyDunn , what about this? Can we make a version of 6.0.0?