Fix: revert hard-coded Android buildrev

MobileLibrary/Android/make.bash

@@ -18,7 +18,7 @@ export GOCACHE=/tmp
 BUILDINFOFILE="psiphon-tunnel-core_buildinfo.txt"
 BUILDDATE=$(date --iso-8601=seconds)
 BUILDREPO="https://github.com/Psiphon-Labs/psiphon-tunnel-core.git"
-BUILDREV="5641695f"
+BUILDREV=$(git rev-parse --short HEAD)
 GOVERSION=$(go version | perl -ne '/go version (.*?) / && print $1')
 
 LDFLAGS="\