Bump ubuntu from `8a37d68` to `dfc1087` in /docker/seacas #754

Job	Run time
build-deps (gnu, 4.9.2)	30s
build-deps (clang, 4.9.2)	30s
build-deps (mpi, 4.9.2)	44s
Debug serial build	4m 18s
Debug parallel build	4m 56s
Use modern CMake configure of netCDF package	6m 16s
	17m 14s

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