upgrade r-base to R 3.4.4 released yesterday

library/r-base

@@ -1,5 +1,5 @@
 # maintainer: "Carl Boettiger" <[email protected]> (@cboettig)
 # maintainer: "Dirk Eddelbuettel" <[email protected]> (@eddelbuettel)
 
-3.4.3: git://github.com/rocker-org/rocker@3019a8c8c29d9337c23e30ef42fa0c6677a0e264 r-base
-latest: git://github.com/rocker-org/rocker@3019a8c8c29d9337c23e30ef42fa0c6677a0e264 r-base
+3.4.4: git://github.com/rocker-org/rocker@151274f9052f874034489769b94eba834309dc5d r-base
+latest: git://github.com/rocker-org/rocker@151274f9052f874034489769b94eba834309dc5d r-base