add sleep before refresh (#45)

Author: jacobfilik

swmr_tools/datasource.py

@@ -289,6 +289,7 @@ def read_frame(self, index, force_refresh=False):
             pos = self.get_pos(index, shape)
         except ValueError:
             # refresh dataset and try again
+            sleep(1)
             refresh_dataset(ds)
 
             shape = ds.shape