fix spelling error in NetworkFileSharesAllowed policy

Bug: None
Change-Id: I671b521dfc6bc34214d680aec2556584820dd18c
Reviewed-on: https://chromium-review.googlesource.com/1181525Reviewed-by: Pavol Marko <pmarko@chromium.org>
Commit-Queue: Bailey Berro <baileyberro@chromium.org>
Cr-Commit-Position: refs/heads/master@{#584536}

components/policy/resources/policy_templates.json

@@ -12668,7 +12668,7 @@
         'per_profile': True,
       },
       'supported_on': ['chrome_os:70-'],
-      'caption': '''Contorls Network File Shares for ChromeOS availibility''',
+      'caption': '''Contorls Network File Shares for ChromeOS availability''',
       'example_value': True,
       'desc': '''This policy controls whether the Network File Shares feature for <ph name="PRODUCT_NAME">$2<ex>Google Chrome OS</ex></ph> is allowed for a user.