fix broken links (prebid#1420)

Author: jeanstemp

formats/formats.md

@@ -60,7 +60,7 @@ A multi-format ad unit supports at least two of the following types: banner, nat
 
 Interstitial ads appear as full screen ads in mobile apps that must be dismissed for interaction with the app to continue. Prebid Mobile supports header bidding for interstitial ads.
 
-- [Prebid Mobile Overview]({site.baseurl}}/prebid-mobile/prebid-mobile.html)
-- [Getting Started with Prebid Mobile]({site.baseurl}}/prebid-mobile/prebid-mobile-pbs.html)
-- [iOS Code Integration]({site.baseurl}}/prebid-mobile/code-integration-ios.html)
-- [Android Code Integration]({site.baseurl}}/prebid-mobile/code-integration-android.html)
+- [Prebid Mobile Overview]({{site.baseurl}}/prebid-mobile/prebid-mobile.html)
+- [Getting Started with Prebid Mobile]({{site.baseurl}}/prebid-mobile/prebid-mobile-pbs.html)
+- [iOS Code Integration]({{site.baseurl}}/prebid-mobile/code-integration-ios.html)
+- [Android Code Integration]({{site.baseurl}}/prebid-mobile/code-integration-android.html)