generate strings (#71)

## Before this PR
We would generate key types by resolving the type of the key. This caused definitions with  maps containing booleans and doubles as keys to generate invalid TypeScript.

## After this PR
We fall back to string on any type which is not a string or an enum

src/commands/generate/tsTypeVisitor.ts

@@ -56,15 +56,14 @@ export class TsTypeVisitor implements ITypeVisitor<string> {
         }
     };
     public map = (obj: IMapType): string => {
-        const keyTsType = IType.visit(obj.keyType, this);
         const valueTsType = IType.visit(obj.valueType, this);
         if (IType.isReference(obj.keyType)) {
             const keyTypeDefinition = this.knownTypes.get(createHashableTypeName(obj.keyType.reference));
             if (keyTypeDefinition != null && ITypeDefinition.isEnum(keyTypeDefinition)) {
                 return `{ [key in ${obj.keyType.reference.name}]?: ${valueTsType} }`;
             }
         }
-        return `{ [key: ${keyTsType}]: ${valueTsType} }`;
+        return `{ [key: string]: ${valueTsType} }`;
     };
     public list = (obj: IListType): string => {
         const itemType = IType.visit(obj.itemType, this);