Update pmp_parameter.py

Author: kristinchang3

pcmdi_metrics/utils/pmp_parameter.py

@@ -3,7 +3,8 @@
 
 import pcmdi_metrics.utils as cdp
 from pcmdi_metrics import LOG_LEVEL
-from pcmdi_metrics.utils import StringConstructor
+
+from . import StringConstructor
 
 try:
     basestring  # noqa