JuMPeR v0.6.0

Update for JuMP v0.18 on julia 1.0 (#82)

* update for julia 1.0

* update travis script

* add LinearAlgebra to REQUIRE

* some updates

* more changes

* add constructors

* define constructor for numbers too

* don't broadcast over norm expressions

* revert to map

* switch back to working version of GLPK

* comment out flakey test for now

it is correct, but the GLPK solver has been problematic on it. see
* https://github.com/IainNZ/JuMPeR.jl/pull/74#issuecomment-292021678
and
*
https://github.com/IainNZ/JuMPeR.jl/pull/74/commits/8327d3648b0aa59f5355
f9bd56b65e8dda6fa642
for workarounds in the past.

* test on different versions of julia

JuMPeR v0.5.0

Merge pull request #71 from IainNZ/require2

change upperbound to jump 0.15