Make Phoenix-frc-lib depend directly on 2018 wpilib

It has binaries which are only compatible with this version, so make the
dependency explicit to untangle upgrades.

Change-Id: I9487a9de46d690477fe5fa9ecae8314d56a853b4
diff --git a/third_party/Phoenix-frc-lib/BUILD b/third_party/Phoenix-frc-lib/BUILD
index 4686b68..dcfd0dc 100644
--- a/third_party/Phoenix-frc-lib/BUILD
+++ b/third_party/Phoenix-frc-lib/BUILD
@@ -38,6 +38,6 @@
     restricted_to = ["//tools:roborio"],
     visibility = ["//visibility:public"],
     deps = [
-        "//third_party:wpilib",
+        "//third_party/allwpilib_2018:hal",
     ],
 )