Fix gr-diff-preferences dialog shows wrong checkbox states after reopen

checkbox input has "checked" attribute and "checked" property. The
checked attribute defines the initial state of a checkbox (when it is
shown for the first time). The checked property defines the current
state of the checkbox. The gr-diff-preferences incorrectly used
attribute binding instead of property binding.

Change-Id: Iaf70b8ebb34d118b17d7782534aea925d4221225
diff --git a/polygerrit-ui/app/elements/shared/gr-diff-preferences/gr-diff-preferences_html.ts b/polygerrit-ui/app/elements/shared/gr-diff-preferences/gr-diff-preferences_html.ts
index f9d971d..54022ba 100644
--- a/polygerrit-ui/app/elements/shared/gr-diff-preferences/gr-diff-preferences_html.ts
+++ b/polygerrit-ui/app/elements/shared/gr-diff-preferences/gr-diff-preferences_html.ts
@@ -49,7 +49,7 @@
         <input
           id="lineWrappingInput"
           type="checkbox"
-          checked$="[[diffPrefs.line_wrapping]]"
+          checked="[[diffPrefs.line_wrapping]]"
           on-change="_handleLineWrappingTap"
         />
       </span>
@@ -132,7 +132,7 @@
         <input
           id="showTabsInput"
           type="checkbox"
-          checked$="[[diffPrefs.show_tabs]]"
+          checked="[[diffPrefs.show_tabs]]"
           on-change="_handleShowTabsTap"
         />
       </span>
@@ -143,7 +143,7 @@
         <input
           id="showTrailingWhitespaceInput"
           type="checkbox"
-          checked$="[[diffPrefs.show_whitespace_errors]]"
+          checked="[[diffPrefs.show_whitespace_errors]]"
           on-change="_handleShowTrailingWhitespaceTap"
         />
       </span>
@@ -154,7 +154,7 @@
         <input
           id="syntaxHighlightInput"
           type="checkbox"
-          checked$="[[diffPrefs.syntax_highlighting]]"
+          checked="[[diffPrefs.syntax_highlighting]]"
           on-change="_handleSyntaxHighlightTap"
         />
       </span>
@@ -165,7 +165,7 @@
         <input
           id="automaticReviewInput"
           type="checkbox"
-          checked$="[[!diffPrefs.manual_review]]"
+          checked="[[!diffPrefs.manual_review]]"
           on-change="_handleAutomaticReviewTap"
         />
       </span>