bump version to 0.6.8

Author: briangu

setup.py

@@ -27,7 +27,7 @@
 setup(
     name='klongpy',
     packages=find_packages(),
-    version='0.6.7',
+    version='0.6.8',
     description='High-Performance Klong array language with rich Python integration.',
     author='Brian Guarraci',
     license='MIT',