Changes to make R package build on windows without warnings

R/DESCRIPTION

@@ -7,10 +7,10 @@ Authors@R: c(
   person("Ben", "Letham", email = "bletham@fb.com", role = "aut")
   )
 Description: Implements a procedure for forecasting time series data based on
-  an additive model where non-linear trends are fit with yearly and weekly
-  seasonality, plus holidays.  It works best with daily periodicity data with
-  at least one year of historical data.  Prophet is robust to missing data,
-  shifts in the trend, and large outliers.
+    an additive model where non-linear trends are fit with yearly and weekly
+    seasonality, plus holidays.  It works best with daily periodicity data with
+    at least one year of historical data.  Prophet is robust to missing data,
+    shifts in the trend, and large outliers.
 Depends:
     R (>= 3.2.3),
     Rcpp (>= 0.12.0)
@@ -31,3 +31,4 @@ License: BSD_3_clause + file LICENSE
 LazyData: true
 RoxygenNote: 6.0.1
 VignetteBuilder: knitr
+SystemRequirements: C++11

R/src/Makevars.win

@@ -1 +1 @@
-
+CXX_STD = CXX11