Fix invalid URL on all requests

[Fabricio20]

This PR fixes an Invalid URL issue that is currently happening on Patreon-Java.

java.io.FileNotFoundException: https://www.patreon.com/api/oauth2/api//campaigns/123123/pledges?page%5Bcount%5D=15
    at sun.net.www.protocol.http.HttpURLConnection.getInputStream0(HttpURLConnection.java:1915)
    at sun.net.www.protocol.http.HttpURLConnection.getInputStream(HttpURLConnection.java:1515)
    at sun.net.www.protocol.https.HttpsURLConnectionImpl.getInputStream(HttpsURLConnectionImpl.java:251)
    at com.patreon.resources.RequestUtil.request(RequestUtil.java:26)
    at com.patreon.PatreonAPI.getDataStream(PatreonAPI.java:201)
    at com.patreon.PatreonAPI.fetchPageOfPledges(PatreonAPI.java:156)
    at com.patreon.PatreonAPI.fetchPageOfPledges(PatreonAPI.java:129)
    at com.patreon.PatreonAPI.fetchAllPledges(PatreonAPI.java:189)

This path issue has been present on Patreon-Java for a long time now but Patreon API never had issues with it, recently however, I started to receive a FileNotFound/404 on the URL because of that extra / in there.

[decmurphy]

+1

This is happening to me now too since I've migrated from Java 8 to 11

Edit: Digging further, it looks like a more specific version of my earlier message would be to say that it works fine on httpclient-4.5.6 but is broken on httpclient-4.5.10 because of how URIBuilder works. Specifially, URIBuilder.buildString() stopped using a method normalizePath() which decided on whether or not to add a leading slash.

So this is not really something that can be changed in this repo since fixing it for some will break it for others. Repo needs to package up its dependencies.