Resolve LoadingBar accessibility issue

- Add an aria-label to the b-progress-bar component to meet
accessibility guidelines
- Nest b-progess-bar component in b-progress component in order to add
aria-label to the correct element

Signed-off-by: Derick Montague <derick.montague@ibm.com>
Change-Id: I3b7d23026d4bcdb607fdbad24170e38116a7eb8a
diff --git a/src/locales/en-US.json b/src/locales/en-US.json
index 4306534..fd97837 100644
--- a/src/locales/en-US.json
+++ b/src/locales/en-US.json
@@ -20,7 +20,8 @@
     },
     "ariaLabel": {
       "showPassword": "Show password as plain text. Note: this will visually expose your password on the screen.",
-      "tooltip": "Tooltip"
+      "tooltip": "Tooltip",
+      "progressBar": "Page loading progress bar"
     },
     "calendar": {
       "openDatePicker": "Open date picker",