Update runtime.txt

benjaminmoon · web-flow · commit 41ccfd3752df · 2021-02-19T16:13:51.000Z
add R version as e.g. <https://github.com/binder-examples/r/blob/master/runtime.txt>
diff --git a/runtime.txt b/runtime.txt
@@ -1 +1 @@
-r-2021-02-18
+r-3.6-2021-02-18
