add missing zlib dependency for NSS

[boegel]

No description provided.

[boegel]

Test report by @boegel
SUCCESS
Build succeeded for 2 out of 2 (2 easyconfigs in this PR)
node3102.skitty.os - Linux centos linux 7.5.1804, Intel(R) Xeon(R) Gold 6140 CPU @ 2.30GHz, Python 2.7.5
See https://gist.github.com/e3093eed1fb7c453b252ea43cd243bc8 for a full test report.

[boegel]

Test report by @boegel
SUCCESS
Build succeeded for 2 out of 2 (2 easyconfigs in this PR)
node2613.swalot.os - Linux centos linux 7.5.1804, Intel(R) Xeon(R) CPU E5-2660 v3 @ 2.60GHz, Python 2.7.5
See https://gist.github.com/39e069eb300c2b1147f488504f06d80d for a full test report.

[boegel]

Test report by @boegel
SUCCESS
Build succeeded for 2 out of 2 (2 easyconfigs in this PR)
node2082.delcatty.os - Linux centos linux 7.5.1804, Intel(R) Xeon(R) CPU E5-2670 0 @ 2.60GHz, Python 2.7.5
See https://gist.github.com/c84fcf9784d567588ac9fefd16c19735 for a full test report.

[vanzod]

Re-trigger Travis

[vanzod]

Test report by @vanzod
SUCCESS
Build succeeded for 3 out of 3 (2 easyconfigs in this PR)
cermis - Linux debian 9.5, Intel(R) Xeon(R) CPU E5620 @ 2.40GHz, Python 2.7.13
See https://gist.github.com/6ec0e536578925b167d8b2a05bf5804f for a full test report.

[vanzod]

Going in, thanks @boegel!