Update root version to v6_18_02a.#102

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hgreenlee wants to merge 4 commits into

LArbys:ups_larbysfrom

hgreenlee:ups_larbys

Commits on Sep 13, 2019

Update root version to v6_18_02a.
hgreenlee
committed

Commits on Sep 23, 2019

Update root version to v6_18_04.
hgreenlee
committed

Commits on Sep 24, 2019

Switch to link using clang for c2.
hgreenlee
committed

Commits on Jan 21, 2020

Merge remote-tracking branch 'larcv/ups_larbys' into ups_larbys
hgreenlee
committed