Update en.xaml

In standard title case (used for buttons and such), articles or short function words like "a" or "for" shouldn't be capitalized. 

Doesn't seem to be capitalized for stylistic reasons either as "Check for Updates" is capitalized in standard title case.

Author: 90gq29

Flow.Launcher/Languages/en.xaml

@@ -449,7 +449,7 @@
     <system:String x:Key="icons">Icons</system:String>
     <system:String x:Key="about_activate_times">You have activated Flow Launcher {0} times</system:String>
     <system:String x:Key="checkUpdates">Check for Updates</system:String>
-    <system:String x:Key="BecomeASponsor">Become A Sponsor</system:String>
+    <system:String x:Key="BecomeASponsor">Become a Sponsor</system:String>
     <system:String x:Key="newVersionTips">New version {0} is available, would you like to restart Flow Launcher to use the update?</system:String>
     <system:String x:Key="checkUpdatesFailed">Check updates failed, please check your connection and proxy settings to api.github.com.</system:String>
     <system:String x:Key="downloadUpdatesFailed">