vendor: Add maintainer for LG G3 (Sprint) (LS990)

Change-Id: I23b4bbc9ffeb6a31bd5f087ba36b6e1df2836fec
diff --git a/CONTRIBUTORS.mkdn b/CONTRIBUTORS.mkdn
index a8ae2d4..401e100 100644
--- a/CONTRIBUTORS.mkdn
+++ b/CONTRIBUTORS.mkdn
@@ -58,7 +58,7 @@
 * __LG G3 (Canada) (D852):__ cuzz1369
 * __LG G3 (International) (D855):__ finnq
 * __LG G3 (Korea) (F400):__ TheNoFace
-* __LG G3 (Sprint) (LS990):__
+* __LG G3 (Sprint) (LS990):__ Kasual
 * __LG G3 (Verizon) (VS985):__ invisiblek
 * __LG G4 (T-Mobile) (H811):__ codeworkx, genesixxbf3
 * __LG G4 (International) (H815):__ codeworkx, genesixxbf3