Nil pointer

[dpengftw]

My guess is that the API calls are reaching a rate limit, therefore the code is running into nil pointer.

Solution would be to use a backoff function to call AWS api, if the first call fails.

`> ecsgo
? Select a task: panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x2 addr=0x0 pc=0x102fdafac]

goroutine 18 [running]:
github.com/tedsmitt/ecsgo/internal.getPlatformFamily({0x103619a00, 0x1400011a100}, {0x1034115e0?, 0x140004ded80?}, 0x140004c8900)
github.com/tedsmitt/ecsgo/internal/internal.go:87 +0x8c
github.com/tedsmitt/ecsgo/internal.(*App).getContainerOS(0x140004016b0)
github.com/tedsmitt/ecsgo/internal/app.go:426 +0xa0
github.com/tedsmitt/ecsgo/internal.(*App).getTask(0x140004016b0)
github.com/tedsmitt/ecsgo/internal/app.go:366 +0xb8c
github.com/tedsmitt/ecsgo/internal.(*App).Start.func1()
github.com/tedsmitt/ecsgo/internal/app.go:70 +0x130
created by github.com/tedsmitt/ecsgo/internal.(*App).Start
github.com/tedsmitt/ecsgo/internal/app.go:60 +0x84`