Fix postinstall when nativescript is not in the PATH

In case `nativescript` is not in the PATH variable, trying to execute `nativescript --version` will fail and the rest of the postinstall will not be executed.
For example on many test environments, where different CLI versions are tested, CLI is installed in a directory and executed directly from there.
Also this breaks adding the plugin with AppBuilder CLI (and other AppBuilder clients).

So try-catch the execution.

Author: rosen-vladimirov

scripts/postinstall.js

@@ -2741,28 +2741,28 @@ function read (opts, cb) {
   \***********************************/
 /***/ (function(module, exports) {
 
-module.exports = function(module) {
-	if(!module.webpackPolyfill) {
-		module.deprecate = function() {};
-		module.paths = [];
-		// module.parent = undefined by default
-		if(!module.children) module.children = [];
-		Object.defineProperty(module, "loaded", {
-			enumerable: true,
-			get: function() {
-				return module.l;
-			}
-		});
-		Object.defineProperty(module, "id", {
-			enumerable: true,
-			get: function() {
-				return module.i;
-			}
-		});
-		module.webpackPolyfill = 1;
-	}
-	return module;
-};
+module.exports = function(module) {
+	if(!module.webpackPolyfill) {
+		module.deprecate = function() {};
+		module.paths = [];
+		// module.parent = undefined by default
+		if(!module.children) module.children = [];
+		Object.defineProperty(module, "loaded", {
+			enumerable: true,
+			get: function() {
+				return module.l;
+			}
+		});
+		Object.defineProperty(module, "id", {
+			enumerable: true,
+			get: function() {
+				return module.i;
+			}
+		});
+		module.webpackPolyfill = 1;
+	}
+	return module;
+};
 
 
 /***/ }),
@@ -2845,17 +2845,24 @@ function readConfig() {
 }
 
 // workaround for https://github.com/NativeScript/nativescript-cli/issues/2521 (2.5.0 only)
-var nativeScriptVersion = __webpack_require__(/*! child_process */ 2).execSync('nativescript --version');
-var promptSupported = nativeScriptVersion.indexOf("2.5.0") === -1;
+var nativeScriptVersion = "";
+try {
+    nativeScriptVersion = __webpack_require__(/*! child_process */ 2).execSync('nativescript --version');
+} catch (err) {
+    // On some environments nativescript is not in the PATH
+    // Ignore the error
+}
+
+var isNativeScriptCLI250 = nativeScriptVersion.indexOf("2.5.0") !== -1;
 
 // note that for CI builds you want a pluginConfigFile, otherwise the build will fail
-if (process.argv.indexOf("config") == -1 && fs.existsSync(pluginConfigPath)) {
+if (process.argv.indexOf("config") === -1 && fs.existsSync(pluginConfigPath)) {
     readConfig();
     console.log("Config file exists (" + pluginConfigFile + ")");
     askiOSPromptResult(config);
     askAndroidPromptResult(config);
     promptQuestionsResult(config);
-} else if (!promptSupported && process.argv.indexOf("setup") == -1) {
+} else if (isNativeScriptCLI250 && process.argv.indexOf("setup") === -1) {
     console.log("*******************************************************************");
     console.log("*******************************************************************");
     console.log("************************** IMPORTANT: *****************************");
@@ -3155,7 +3162,7 @@ var fs = require("fs");
 module.exports = function() {
 
     console.log("Configure firebase");
-    var buildGradlePath = path.join(__dirname, "..", "..", "platforms", "android", "build.gradle"); 
+    var buildGradlePath = path.join(__dirname, "..", "..", "platforms", "android", "build.gradle");
     if (fs.existsSync(buildGradlePath)) {
         var buildGradleContent = fs.readFileSync(buildGradlePath).toString();