Added quotations to hashtags searches

Since #Hashtags can contain space, using quotation
marks is neccessary when issuing searches from
clicking the #Hashtags in the UI.

Change-Id: I2e07ca354a11092dceaa23691d6d72300d7abbef

gerrit-gwtui/src/main/java/com/google/gerrit/client/change/Hashtags.java

@@ -162,7 +162,8 @@ public class Hashtags extends Composite {
           .setAttribute(DATA_ID, hashtagName)
           .setStyleName(style.hashtagName())
           .openAnchor()
-          .setAttribute("href", "#" + PageLinks.toChangeQuery("hashtag:" + hashtagName))
+          .setAttribute("href",
+              "#" + PageLinks.toChangeQuery("hashtag:\"" + hashtagName + "\""))
           .setAttribute("role", "listitem")
           .append("#").append(hashtagName)
           .closeAnchor()