switching date retrieval to use a more robust method

kis_tools/gris/GrisMapExtractor.py

@@ -47,7 +47,7 @@ def get_limits(penfile):
 
 
 class GrisMapExtractor:
-    # class for extracting gris maps form save file in batch
+    # class for extracting gris maps from save file in batch
 
     def __init__(self, path_to_day, outdir):
         """Class to extract maps from IDL save files.  The Class is
@@ -76,7 +76,7 @@ class GrisMapExtractor:
         # Extract basic info from path and filesystem
         self.path = abspath(path_to_day)
         self.folder_name = basename(self.path)
-        self.date = datetime.datetime.strptime(self.folder_name.split("_")[0], "%Y%m%d")
+        self.date = date_from_fn(self.folder_name)
 
         # Setup paths to subfolders:
         self.outdir = join(outdir, "context_data")