Fix typo in models/small_strato.def comments

"et" should be "set".  Should have been added to prior commit but
was left out.

Signed-off-by: Bob Yantosca <yantosca@seas.harvard.edu>

models/small_strato.def

@@ -7,7 +7,7 @@
 #CHECK O; N;                    { Check Mass Balance of oxygen & nitrogen }
 
 #INITVALUES                     { Set initial values of species           }
-  CFACTOR = 1.    ;             { and et units conversion factor to 1     }
+  CFACTOR = 1.    ;             { and set units conversion factor to 1    }
   O1D = 9.906E+01 ;
   O   = 6.624E+08 ;
   O3  = 5.326E+11 ;