Use python3 instead of python on non-windows machines.

.travis.yml

@@ -11,3 +11,4 @@ install:
 
 script:
   - npm run test
+  - npm run build

package.json

@@ -17,8 +17,8 @@
 		"test": "mocha test",
 		"coverage": "nyc mocha test",
 		"codecov": "nyc --reporter=lcov mocha test && codecov",
-		"build": "python tools/create_package.py",
-		"update": "python tools/update_includes.py",
-		"svg": "python tools/optimize_svg_files.py"
+		"build": "node tools/run_python.js tools/create_package.py",
+		"update": "node tools/run_python.js tools/update_includes.py",
+		"svg": "node tools/run_python.js tools/optimize_svg_files.py"
 	}
 }

tools/run_python.js

@@ -0,0 +1,8 @@
+let cp = require ('child_process');
+let pythonExecutable = 'python';
+if (process.platform != 'win32') {
+    pythonExecutable = 'python3';
+}
+cp.spawnSync ('python', process.argv.slice (2), {
+    stdio: "inherit"
+});