fix appveyor build of es6

appveyor.yml

@@ -16,7 +16,7 @@ build_script:
 after_build: 
   - msbuild /target:pack /property:Configuration=Release /verbosity:detailed runtime/CSharp/runtime/CSharp/Antlr4.dotnet.sln
 test_script:
-  - mvn install -Dantlr-php-php="C:\tools\php\php.exe" -Dantlr-dart-dart="C:\tools\dart-sdk\bin\dart.exe" -Dantlr-dart-pub="C:\tools\dart-sdk\bin\pub.bat" -Dantlr-dart-dart2native="C:\tools\dart-sdk\bin\dart2native.bat" -Dantlr-python2-python="C:\Python27\python.exe" -Dantlr-python3-python="C:\Python35\python.exe" -Dantlr-javascript-nodejs="C:\Program Files (x86)\nodejs\node.exe" --batch-mode
+  - mvn install -Dantlr-php-php="C:\tools\php\php.exe" -Dantlr-dart-dart="C:\tools\dart-sdk\bin\dart.exe" -Dantlr-dart-pub="C:\tools\dart-sdk\bin\pub.bat" -Dantlr-dart-dart2native="C:\tools\dart-sdk\bin\dart2native.bat" -Dantlr-python2-python="C:\Python27\python.exe" -Dantlr-python3-python="C:\Python35\python.exe" -Dantlr-javascript-nodejs="C:\Program Files (x86)\nodejs\node.exe" -Dantlr-javascript-npm="C:\Program Files (x86)\nodejs\npm.exe" --batch-mode
 artifacts:
 - path: 'runtime\**\*.nupkg'  
   name: NuGet

runtime-testsuite/test/org/antlr/v4/test/runtime/javascript/BaseNodeTest.java

@@ -362,16 +362,6 @@ public class BaseNodeTest implements RuntimeTestSupport {
 			throw new IOException("'npm link antlr4' failed");
 	}
 
-	private String locateTool(String tool) {
-		String[] roots = { "/usr/bin/", "/usr/local/bin/" };
-		for (String root : roots) {
-			if (new File(root + tool).exists()) {
-				return root + tool;
-			}
-		}
-		return null;
-	}
-
 	private boolean canExecute(String tool) {
 		try {
 			ProcessBuilder builder = new ProcessBuilder(tool, "--version");
@@ -391,6 +381,11 @@ public class BaseNodeTest implements RuntimeTestSupport {
 	}
 
 	private String locateNpm() {
+		// typically /usr/local/bin/npm
+		String prop = System.getProperty("antlr-javascript-npm");
+		if ( prop!=null && prop.length()!=0 ) {
+			return prop;
+		}
 		return "npm"; // everywhere
 	}