Update navigation arrows

Update arrows to match the original Bootstrap style according to docs:
http://getbootstrap.com/components/#pagination

src/bootstrap-table.js

@@ -168,10 +168,10 @@
         paginationHAlign: 'right', //right, left
         paginationVAlign: 'bottom', //bottom, top, both
         paginationDetailHAlign: 'left', //right, left
-        paginationFirstText: '<<',
-        paginationPreText: '<',
-        paginationNextText: '>',
-        paginationLastText: '>>',
+        paginationFirstText: '«',
+        paginationPreText: '‹',
+        paginationNextText: '›',
+        paginationLastText: '»',
         search: false,
         searchAlign: 'right',
         selectItemName: 'btSelectItem',