Merge pull request #244 from richfitz/use-cpp11

Use C++11 for compilation

Author: Raphael Sonabend

DESCRIPTION

@@ -1,6 +1,6 @@
 Package: distr6
 Title: The Complete R6 Probability Distributions Interface
-Version: 1.5.1
+Version: 1.5.2
 Authors@R:
       c(person(given = "Raphael",
              family = "Sonabend",
@@ -95,6 +95,7 @@ VignetteBuilder:
 Encoding: UTF-8
 Roxygen: list(markdown = TRUE, r6 = TRUE)
 RoxygenNote: 7.1.1
+SystemRequirements: C++11
 Collate:
     'helpers.R'
     'distr6_globals.R'