Make LetterTileDrawables bold

Bug: 24682810
Change-Id: I044ec6e04d998b790913e245d8815c291ac869d3
diff --git a/res-common/values/strings.xml b/res-common/values/strings.xml
index e3fc643..fab8e97 100644
--- a/res-common/values/strings.xml
+++ b/res-common/values/strings.xml
@@ -730,7 +730,7 @@
 
     <!-- Font family used when drawing letters for letter tile avatars.
          Do not translate. -->
-    <string name="letter_tile_letter_font_family">sans-serif-light</string>
+    <string name="letter_tile_letter_font_family">sans-serif-medium</string>
 
     <!-- Content description for the fake action menu up button as used
      inside search. [CHAR LIMIT=NONE] -->