Added plaintext signature for Yammer Api and fixed fucked up indentation

src/main/java/org/scribe/builder/api/YammerApi.java

@@ -1,26 +1,33 @@
 package org.scribe.builder.api;
 
-import org.scribe.model.Token;
+import org.scribe.model.*;
+import org.scribe.services.*;
 
 public class YammerApi extends DefaultApi10a
 {
   private static final String AUTHORIZATION_URL = "'https://www.yammer.com/oauth/authorize?oauth_token=%s'";
 
-	@Override
-	public String getRequestTokenEndpoint()
+  @Override
+  public String getRequestTokenEndpoint()
   {
-		return "https://www.yammer.com/oauth/request_token";
-	}
+    return "https://www.yammer.com/oauth/request_token";
+  }
 
-	@Override
-	public String getAccessTokenEndpoint()
+  @Override
+  public String getAccessTokenEndpoint()
   {
-		return "https://www.yammer.com/oauth/access_token";
-	}
-	
-	@Override
-	public String getAuthorizationUrl(Token requestToken)
-	{
-	  return String.format(AUTHORIZATION_URL, requestToken.getToken());
-	}
+    return "https://www.yammer.com/oauth/access_token";
+  }
+
+  @Override
+  public String getAuthorizationUrl(Token requestToken)
+  {
+    return String.format(AUTHORIZATION_URL, requestToken.getToken());
+  }
+
+  @Override
+  public SignatureService getSignatureService()
+  {
+    return new PlaintextSignatureService();
+  }
 }