provide shape for provider and consumer

use suggestion from @audunru from #94

Author: judithhartmann

index.d.ts

@@ -7,6 +7,15 @@ declare module 'gatsby-plugin-intl' {
   export class Link<TState> extends gatsby.Link<TState> {}
   export const navigate: typeof gatsby.navigate;
   export const changeLocale: (language: string, to?: string) => void;
-  export const IntlContextProvider: React.Provider<any>;
-  export const IntlContextConsumer: React.Consumer<any>;
+  
+  import { IntlShape } from "react-intl";
+  interface GatsbyPluginIntlShape extends IntlShape {
+    language: string;
+    languages: string[];
+    routed: boolean;
+    originalPath: string;
+    redirect: boolean;
+  }
+  export const IntlContextProvider: React.Provider<GatsbyPluginIntlShape>;
+  export const IntlContextConsumer: React.Consumer<GatsbyPluginIntlShape>;
 }