Update _classes.py

amend delta2-delta1

Author: sangyu

dabest/_classes.py

@@ -888,7 +888,7 @@ class DeltaDelta(object):
 
     .. math::
 
-        \\Delta_{\\Delta} = \\Delta_{B_{2}} - \\Delta_{B_{1}}
+        \\Delta_{\\Delta} = \\Delta_{2} - \\Delta_{1}
     
     and:
 
@@ -3467,4 +3467,4 @@ def permutations_var(self):
         """
         The experiment group variance of all the permutations in a list.
         """
-        return self.__permutations_var
+        return self.__permutations_var