Fix: Correcting syntax issue in SConstruct

There is a compilation error found, when building this library using
scons. Used the latest version of scons v4.9.0 and the python version
3.9.21

Author: Sagovind

SConstruct

@@ -32,7 +32,7 @@ elif os.environ.has_key('BOOST_INCLUDES') and os.environ.has_key('BOOST_LIBS'):
    env['BOOST_INCLUDES'] = os.environ['BOOST_INCLUDES']
    env['BOOST_LIBS'] = os.environ['BOOST_LIBS']
 else:
-   raise SCons.Errors.UserError, "Neither BOOST_ROOT, nor BOOST_INCLUDES + BOOST_LIBS was set!"
+   raise SCons.Errors.UserError("Neither BOOST_ROOT, nor BOOST_INCLUDES + BOOST_LIBS was set!")
 
 ## Custom OpenSSL
 if os.environ.has_key('OPENSSL_PATH'):