[WAGON-540] Switch to modern-day encoding (UTF-8) of auth credentials

Unfortunately, no test can be added because Jetty's default
BasicAuthenticator uses ISO-8859-1 hardcoded and this cannot be changed.
Nexus uses Shiro which decodes as UTF-8 by default.
diff --git a/wagon-providers/wagon-http-shared/src/main/java/org/apache/maven/wagon/shared/http/AbstractHttpClientWagon.java b/wagon-providers/wagon-http-shared/src/main/java/org/apache/maven/wagon/shared/http/AbstractHttpClientWagon.java
index 47f1794..5b909bb 100755
--- a/wagon-providers/wagon-http-shared/src/main/java/org/apache/maven/wagon/shared/http/AbstractHttpClientWagon.java
+++ b/wagon-providers/wagon-http-shared/src/main/java/org/apache/maven/wagon/shared/http/AbstractHttpClientWagon.java
@@ -93,6 +93,7 @@
 import java.nio.ByteBuffer;
 import java.nio.channels.Channels;
 import java.nio.channels.ReadableByteChannel;
+import java.nio.charset.StandardCharsets;
 import java.text.SimpleDateFormat;
 import java.util.ArrayList;
 import java.util.Collection;
@@ -453,8 +454,8 @@
     private static Registry<AuthSchemeProvider> createAuthSchemeRegistry()
     {
         return RegistryBuilder.<AuthSchemeProvider>create()
-            .register( AuthSchemes.BASIC, new BasicSchemeFactory() )
-            .register( AuthSchemes.DIGEST, new DigestSchemeFactory() )
+            .register( AuthSchemes.BASIC, new BasicSchemeFactory( StandardCharsets.UTF_8 ) )
+            .register( AuthSchemes.DIGEST, new DigestSchemeFactory( StandardCharsets.UTF_8 ) )
             .register( AuthSchemes.NTLM, new NTLMSchemeFactory() )
             .build();
     }