Fix compiler error by adding 'try!'

[stevebroshar]

Master branch does not compile due to build error:

Swift Compiler Error (Xcode): Call can throw, but it is not marked with 'try' and the error is not handled
/Users/stevebroshar/code/tremor_poc_app/ios/Pods/MetaWear/MetaWear/DFU/FirmwareBuild.swift:88:35
Swift Compiler Error (Xcode): Call can throw, but it is not marked with 'try' and the error is not handled
/Users/stevebroshar/code/tremor_poc_app/ios/Pods/MetaWear/MetaWear/DFU/FirmwareBuild.swift:90:35

This change adds 'try!' to eliminate this error. Honestly, I don't know whether this is a good way to fix. But, it's surely better to compile than to not.