Clean up selectors

Some syntax cleanup for the jQuery 1.8 upgrade:
- Moving ':first' selector to the end of the chain (similar to
  g/338660)
- Remove extra " (similar to g/339172)

refs FOO-4220
flag=none

Test Plan:
- Jenkins passes

Change-Id: I004a9c547c04418279b5474b4f1dd35ec8fd6c5c
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/339133
Tested-by: Service Cloud Jenkins <svc.cloudjenkins@instructure.com>
Reviewed-by: Michael Hulse <michael.hulse@instructure.com>
QA-Review: Angela Gomba <angela.gomba@instructure.com>
Product-Review: Angela Gomba <angela.gomba@instructure.com>

spec/selenium/assignments/assignments_overrides_spec.rb

@@ -81,7 +81,7 @@ describe "assignment groups" do
       assign = @course.assignments.create!(title: "due tomorrow", due_at: 2.days.from_now)
       get "/courses/#{@course.id}/assignments/#{assign.id}/edit"
 
-      fj(".date_field:first[data-date-type='due_at']").clear
+      fj(".date_field[data-date-type='due_at']:first").clear
       expect_new_page_load { submit_form("#edit_assignment_form") }
 
       expect(assign.reload.due_at).to be_nil

spec/selenium/assignments/assignments_spec.rb

@@ -317,7 +317,7 @@ describe "assignments" do
           expect_new_page_load { f(".more_options").click }
           expect(f("#assignment_name").attribute(:value)).to include(expected_text)
           expect(f("#assignment_points_possible").attribute(:value)).to include(points)
-          due_at_field = fj(".date_field:first[data-date-type='due_at']")
+          due_at_field = fj(".date_field[data-date-type='due_at']:first")
           expect(due_at_field).to have_value due_at
           click_option("#assignment_submission_type", "No Submission")
           submit_assignment_form

ui/shared/rubrics/jquery/edit_rubric.jsx

@@ -78,7 +78,7 @@ const rubricEditing = {
         document.getElementById('add_criterion_container')
       )
       if (focusTarget) {
-        $rubric.find(`"#add_criterion_container ${focusTarget}:visible`).focus()
+        $rubric.find(`#add_criterion_container ${focusTarget}:visible`).focus()
       }
     }, 0)
   },