Enforce supported versions of node and npm
Enforce supported versions of node and npm

This package uses node features which require node v6.x and higher.
Prior to this change the package would install but a user would
get runtime errors for constructs (e.g. class) which are not
natively supported in prior version of node.  For compatibility with
prior versions of npm < 3.0.0, included both the "engine-strict" and
"engineStrict" (deprecated) flags.

Fixes FAB-725

Change-Id: Ib7042ecdec51bdcfddbd6be23f69d5391519572d
Signed-off-by: Gari Singh <10008a422f4be611b73174084ba2f7f909d5b402@gmail.com>

ratnakar-asara/fabric-sdk-node,adityachap/fabric-sdk-node,adityachap/fabric-sdk-node,ratnakar-asara/fabric-sdk-node,ratnakar-asara/fabric-sdk-node,rennman/updateNodeSdkUT,rennman/updateNodeSdkUT,ratnakar-asara/fabric-sdk-node,cdaughtr/fabric-sdk-node-docs