Update headings for Android requirements section (#211)

Author: sekodev

markdown/plugin/ageRange/index.markdown

@@ -87,12 +87,14 @@ settings =
 
 ### Android Requirements
 
-#### Google Play Store Builds
+**Google Play Store Builds**
+
 Ensure Google Play Services is up to date. The Age Signals API requires:
 - Google Play Store installed and enabled
 - Google Play Services 22.0.0 or later
 
-#### Amazon Appstore / Fire OS Builds
+**Amazon Appstore / Fire OS Builds**
+
 The Age Range plugin supports Amazon’s GetUserAgeData API on Fire OS devices and any Android device running the Amazon Appstore. Requirements include:
 - Fire OS device or Android device with Amazon Appstore installed
 - Amazon Kids child profile for supervised age range data (otherwise age range may be unavailable)