v3.1.1.0

New:

• Update to Pelion DM Client 3.1.1.0 - https://github.com/ARMmbed/mbed-cloud-client/releases/tag/3.1.1

Fixes:

• Relax timeouts for tests (#91)
• Remove extra space from get request (#94)
• Detect common user errors runtime (#86)
• Fix SPDMC desctructor HardFault (#93)
• Minor doc updates