minor change of name

Author: rcaneill

gsw_xarray/_names.py

@@ -2,8 +2,8 @@
     "CT_first_derivatives": ("CT_SA", "CT_pt"),
     "CT_first_derivatives_wrt_t_exact": ("CT_SA_wrt_t", "CT_T_wrt_t", "CT_P_wrt_t"),
     "CT_freezing": "CT_freezing",
-    "CT_freezing_first_derivatives": ("CTfreezing_SA", "CTfreezing_P"),
-    "CT_freezing_first_derivatives_poly": ("CTfreezing_SA", "CTfreezing_P"),
+    "CT_freezing_first_derivatives": ("CT_freezing_SA", "CT_freezing_P"),
+    "CT_freezing_first_derivatives_poly": ("CT_freezing_SA", "CT_freezing_P"),
     "CT_freezing_poly": "CT_freezing",
     "CT_from_enthalpy": "CT",
     "CT_from_enthalpy_exact": "CT",