Update coordinate_transformations.schema with input_axes and output_axes as strings

Author: will-moore

schemas/coordinate_transformations.schema

@@ -339,14 +339,14 @@
               "input_axes": {
                 "type": "array",
                 "items": {
-                  "type": "number"
+                  "type": "string"
                 },
                 "description": "Names of the input axes for this transformation."
               },
               "output_axes": {
                 "type": "array",
                 "items": {
-                  "type": "number"
+                  "type": "string"
                 },
                 "description": "Names of the output axes for this transformation."
               }