Require nodejs 10 and update build docs (#4805)

docs/BuildFromSource.md

@@ -18,7 +18,7 @@ Building ASP.NET Core on Windows requires:
 * Visual Studio 2017. <https://visualstudio.com>
 * Git. <https://git-scm.org>
 * (Optional) some optional components, like the SignalR Java client, may require
-    * NodeJS <https://nodejs.org>
+    * NodeJS. LTS version of 10.14.2 or newer recommended <https://nodejs.org>
     * Java Development Kit 10 or newer. Either:
         * OpenJDK <http://jdk.java.net/10/>
         * Oracle's JDK <https://www.oracle.com/technetwork/java/javase/downloads/index.html>
@@ -32,7 +32,7 @@ Building ASP.NET Core on macOS or Linux requires:
 * At least 10 GB of disk space and a good internet connection (our build scripts download a lot of tools and dependencies)
 * Git <https://git-scm.org>
 * (Optional) some optional components, like the SignalR Java client, may require
-    * NodeJS  <https://nodejs.org>
+    * NodeJS. LTS version of 10.14.2 or newer recommended <https://nodejs.org>
     * Java Development Kit 10 or newer. Either:
         * OpenJDK <http://jdk.java.net/10/>
         * Oracle's JDK <https://www.oracle.com/technetwork/java/javase/downloads/index.html>

korebuild.json

@@ -4,7 +4,7 @@
   "msbuildType": "full",
   "toolsets": {
     "nodejs": {
-      "minVersion": "8.0",
+      "minVersion": "10.0",
       "required": true
     },
     "visualstudio": {