Add build script and remove babel (#2439)

* Add build script and remove babel

This change adds a build script which uses babel to transpile generated es6 source to es5, such that it can then be used in node projects or published as a package to npm. The `babel` package is also removed as it is deprecated, and superseded by `babel-cli`.

See https://github.com/OpenAPITools/openapi-generator/issues/2126#issuecomment-473926663

* update samples

samples/openapi3/client/petstore/javascript-es6/docs/EnumTest.md

@@ -8,6 +8,9 @@ Name | Type | Description | Notes
 **enumInteger** | **Number** |  | [optional] 
 **enumNumber** | **Number** |  | [optional] 
 **outerEnum** | [**OuterEnum**](OuterEnum.md) |  | [optional] 
+**outerEnumInteger** | [**OuterEnumInteger**](OuterEnumInteger.md) |  | [optional] 
+**outerEnumDefaultValue** | [**OuterEnumDefaultValue**](OuterEnumDefaultValue.md) |  | [optional] 
+**outerEnumIntegerDefaultValue** | [**OuterEnumIntegerDefaultValue**](OuterEnumIntegerDefaultValue.md) |  | [optional] 
 
 
 <a name="EnumStringEnum"></a>

samples/openapi3/client/petstore/javascript-es6/docs/OuterEnumDefaultValue.md

@@ -0,0 +1,12 @@
+# OpenApiPetstore.OuterEnumDefaultValue
+
+## Enum
+
+
+* `placed` (value: `"placed"`)
+
+* `approved` (value: `"approved"`)
+
+* `delivered` (value: `"delivered"`)
+
+

samples/openapi3/client/petstore/javascript-es6/docs/OuterEnumInteger.md

@@ -0,0 +1,12 @@
+# OpenApiPetstore.OuterEnumInteger
+
+## Enum
+
+
+* `0` (value: `0`)
+
+* `1` (value: `1`)
+
+* `2` (value: `2`)
+
+

samples/openapi3/client/petstore/javascript-es6/docs/OuterEnumIntegerDefaultValue.md

@@ -0,0 +1,12 @@
+# OpenApiPetstore.OuterEnumIntegerDefaultValue
+
+## Enum
+
+
+* `0` (value: `0`)
+
+* `1` (value: `1`)
+
+* `2` (value: `2`)
+
+