Drop Julia v0.6 and Julia v0.7

[blegat]

See https://discourse.julialang.org/t/julia-0-6-and-0-7-are-now-officially-unmaintained/20449/2
Dropping a Julia release cannot be done in a patch release so I assign it to the v0.9 milestone.

• Julia v0.6 Remove julia-06 #714
• Julia v0.7 Drop Julia v0.7 #717

[mlubin]

I don't think we should be in a rush to drop 0.6/0.7, but next time we need to make a breaking release we can roll this into it.

[matbesancon]

Fixed in #714

[blegat]

#714 only drops Julia v0.6. Any reason to keep Julia v0.7 ?

[matbesancon]

people still upgrading and not moving "brutally" from 0.6 to 1.0? But you're right we could remove it

[blegat]

Let's divide this issue in two and only drop Julia v0.6 for now

[matbesancon]

agreed