Prepare for 0.3.1-beta release

Rb.Forms.Barcode.nuspec

@@ -3,7 +3,7 @@
   <metadata>
     <id>Rb.Forms.Barcode</id>
     <title>Barcode scanner plugin for Xamarin.Forms</title>
-    <version>0.3.0-beta</version>
+    <version>0.3.1-beta</version>
     <authors>Ota Mares</authors>
     <owners>reBuy reCommerce GmbH</owners>
     <licenseUrl>https://github.com/rebuy-de/rb-forms-barcode/blob/master/LICENSE</licenseUrl>
@@ -14,7 +14,10 @@ Please check the website for further details.
 
 Beta notice: Currently only android is supported.</description>
     <summary>Rb.Forms.Barcode is a Xamarin.Forms view for scanning barcodes.</summary>
-    <releaseNotes>0.3.0-beta
+    <releaseNotes>0.3.1-beta:
+* Fixed: Memory issue when restarting camera.
+
+0.3.0-beta:
 * New: Improved performance by using buffers and FastAndroidCamera.
 * New: Added plenty configuration options!
 * Fixed: Various preview halting and runtime issues.