vim-patch:8.1.1305: there is no easy way to manipulate environment variables

Problem:    There is no easy way to manipulate environment variables.
Solution:   Add environ(), getenv() and setenv(). (Yasuhiro Matsumoto,
            closes vim/vim#2875)
691ddeefb5

src/nvim/eval.lua

@@ -89,6 +89,7 @@ return {
     diff_filler={args=1},
     diff_hlID={args=2},
     empty={args=1},
+    environ={},
     escape={args=2},
     eval={args=1},
     eventhandler={},
@@ -135,6 +136,7 @@ return {
     getcompletion={args={2, 3}},
     getcurpos={},
     getcwd={args={0,2}},
+    getenv={args={1}},
     getfontname={args={0, 1}},
     getfperm={args=1},
     getfsize={args=1},
@@ -274,6 +276,7 @@ return {
     setbufvar={args=3},
     setcharsearch={args=1},
     setcmdpos={args=1},
+    setenv={args=2},
     setfperm={args=2},
     setline={args=2},
     setloclist={args={2, 4}},