Fix syntax error in meta-schema validation example snippet
The previous snippet resulted in the error:
```
invalid character '$' looking for beginning of object key string
```
Rather than the intended error:
```
multipleOf: Invalid type. Expected: number, given: boolean
```
diff --git a/README.md b/README.md
index 758f26d..aa33383 100644
--- a/README.md
+++ b/README.md
@@ -217,7 +217,7 @@
sl := gojsonschema.NewSchemaLoader()
sl.Validate = true
err := sl.AddSchemas(gojsonschema.NewStringLoader(`{
- $id" : "http://some_host.com/invalid.json",
+ "$id" : "http://some_host.com/invalid.json",
"$schema": "http://json-schema.org/draft-07/schema#",
"multipleOf" : true
}`))
