Add update script

nix/sources.json

@@ -2,12 +2,13 @@
     "nixpkgs": {
         "branch": "nixos-19.03",
         "description": "Nixpkgs/NixOS branches that track the Nixpkgs/NixOS channels",
+        "homepage": "https://github.com/NixOS/nixpkgs",
         "owner": "NixOS",
         "repo": "nixpkgs-channels",
-        "rev": "8634c3b619909db7fc747faf8c03592986626e21",
-        "sha256": "0hcpy4q64vbqmlmnfcavfxilyygyzpwdsss8g3p73ikpic0j6ziq",
+        "rev": "5b0b58685d68b9c9c12132f7b392c9dcdecc5931",
+        "sha256": "1fy1ghl79p3w1vg0hnakvrb1lqic4mjrwmylcgqa5bd4ilfrirzf",
         "type": "tarball",
-        "url": "https://github.com/NixOS/nixpkgs-channels/archive/8634c3b619909db7fc747faf8c03592986626e21.tar.gz",
+        "url": "https://github.com/NixOS/nixpkgs-channels/archive/5b0b58685d68b9c9c12132f7b392c9dcdecc5931.tar.gz",
         "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
     },
     "termtosvg": {
@@ -16,10 +17,10 @@
         "homepage": "https://nbedos.github.io/termtosvg/",
         "owner": "nbedos",
         "repo": "termtosvg",
-        "rev": "525330d7d3d7f55b9ed2344140b9b320552a97a4",
-        "sha256": "07y39kyabsz88vrf37chcb0d4s5d6knyg95xmq5787vp987f5ii0",
+        "rev": "b97cc0132073111cec37f64c95539e869202ff99",
+        "sha256": "1c86622sda98zm3q3dzwmm37i09yca661kn860svl191nqbh2l68",
         "type": "tarball",
-        "url": "https://github.com/nbedos/termtosvg/archive/525330d7d3d7f55b9ed2344140b9b320552a97a4.tar.gz",
+        "url": "https://github.com/nbedos/termtosvg/archive/b97cc0132073111cec37f64c95539e869202ff99.tar.gz",
         "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
     }
 }

script/update

@@ -0,0 +1,7 @@
+#!/usr/bin/env nix-shell
+#!nix-shell -I nixpkgs=./nix
+#!nix-shell -i bash -p cabal-install -p nix -p curl --pure
+#!nix-shell --keep SSL_CERT_FILE
+# vim: filetype=sh
+
+$(nix-build -A niv)/bin/niv update