Bump third-party/libswiftnav from 87b9931 to d6a2bbc (#27)

dependabot[bot] · web-flow · commit 162cb6ef315b · 2021-01-13T02:23:23.000Z
diff --git a/third-party/libswiftnav b/third-party/libswiftnav
@@ -1 +1 @@
-Subproject commit 87b99319af01ef582e8c30722072c6171b9a19cf
+Subproject commit d6a2bbc7a1b12f821b2eb059bc926376f606c26c
