Replace struct with map in yaml

Author: jennybuckley

internal/testdata/bad-schema.yaml

@@ -1,6 +1,6 @@
 types:
 - apple: schema
-  struct:
+  map:
     fields:
       - name: types
         type:
@@ -11,7 +11,7 @@ types:
             keys:
             - name
 - name: typeDef
-  struct:
+  map:
     fields:
     - name: name
       type:
@@ -32,7 +32,7 @@ types:
       type:
         namedType: untyped
 - name: typeRef
-  struct:
+  map:
     fields:
     - name: namedType
       type:
@@ -55,7 +55,7 @@ types:
 - name: scalar
   scalar: string
 - name: struct
-  struct:
+  map:
     fields:
     - name: fields
       type:
@@ -68,7 +68,7 @@ types:
       type:
         scalar: string
 - name: structField
-  struct:
+  map:
     fields:
     - name: name
       type:
@@ -77,7 +77,7 @@ types:
       type:
         namedType: typeRef
 - name: list
-  struct:
+  map:
     fields:
     - name: elementType
       type:
@@ -91,7 +91,7 @@ types:
           elementType:
             scalar: string
 - name: map
-  struct:
+  map:
     fields:
     - name: elementType
       type:
@@ -100,7 +100,7 @@ types:
       type:
         scalar: string
 - name: untyped
-  struct:
+  map:
     fields:
     - name: elementRelationship
       type: