FAB-6909 upgrade support to 8.9.0 (new LTS)

node.js just published new LTS with 8.9.0, should upgrade
supported version from the last LTS (6.9.0) to this new
version.

Change-Id: I4ee605459ee745c5af699b5b0168481ba6cf1f05
Signed-off-by: Jim Zhang <jzhang@us.ibm.com>

README.md

@@ -16,8 +16,8 @@ The following section targets a current or future contributor to this project it
 
 ### Build and Test
 To build and test, the following pre-requisites must be installed first:
-* node runtime version 6.9.x or higher, and 8.4.0 or higher ( __Node v7+ is not supported__ )
-* npm tool version 3.10.x or higher
+* node runtime LTS version 8.9.0 or higher, up to 9.0 ( __Node v9.0+ is not supported__ )
+* npm tool version 5.5.1 or higher
 * gulp command (must be installed globaly with `npm install -g gulp`)
 * docker (not required if you only want to run the headless tests with `npm test`, see below)
 

fabric-ca-client/package.json

@@ -7,8 +7,8 @@
     "url": "http://gerrit.hyperledger.org/r/fabric-sdk-node"
   },
   "engines": {
-    "node": ">=6.9.0",
-    "npm": ">=3.10.0"
+    "node": "^8.9.0",
+    "npm": "^5.5.1"
   },
   "dependencies": {
     "bn.js": "^4.11.3",

fabric-client/package.json

@@ -10,8 +10,8 @@
     "test": "node test/unit/headless-tests.js"
   },
   "engines": {
-    "node": ">=6.9.0",
-    "npm": ">=3.10.0"
+    "node": "^8.9.0",
+    "npm": "^5.5.1"
   },
   "dependencies": {
     "bn.js": "^4.11.3",