Extend custom_theme strings length limitation

Bug: 159718432
Test: manually
Change-Id: I2f3aa3102fa762146428ca55cc5e27f1ae3b9c4d
diff --git a/res/values/strings.xml b/res/values/strings.xml
index 1ce95db..b4ec835 100755
--- a/res/values/strings.xml
+++ b/res/values/strings.xml
@@ -121,7 +121,7 @@
         [CHAR LIMIT=20] -->
     <string name="custom_theme_previous">Previous</string>
 
-    <!-- Title for "Custom theme" option. [CHAR LIMIT=15] -->
+    <!-- Title for "Custom theme" option. [CHAR LIMIT=20] -->
     <string name="custom_theme">Custom</string>
 
     <!-- Generic label for one system Style/Theme (combination of fonts/colors/icons) that is