sage: use slightly more robust way of getting threejs version

pkgs/applications/science/math/sage/patches/dont-grep-threejs-version-from-minified-js.patch

@@ -0,0 +1,16 @@
+diff --git a/src/sage/repl/rich_output/display_manager.py b/src/sage/repl/rich_output/display_manager.py
+index fb21f7a9c9..f39470777d 100644
+--- a/src/sage/repl/rich_output/display_manager.py
++++ b/src/sage/repl/rich_output/display_manager.py
+@@ -749,9 +749,9 @@ class DisplayManager(SageObject):
+             import sage.env
+             import re
+             import os
+-            with open(os.path.join(sage.env.THREEJS_DIR, 'build', 'three.min.js')) as f:
++            with open(os.path.join(sage.env.THREEJS_DIR, 'build', 'three.js')) as f:
+                 text = f.read().replace('\n','')
+-            version = re.search(r'REVISION="(\d+)"', text).group(1)
++            version = re.search(r"REVISION = '(\d+)'", text).group(1)
+             return """
+ <script src="https://cdn.jsdelivr.net/gh/mrdoob/three.js@r{0}/build/three.min.js"></script>
+ <script src="https://cdn.jsdelivr.net/gh/mrdoob/three.js@r{0}/examples/js/controls/OrbitControls.js"></script>

pkgs/applications/science/math/sage/sage-src.nix

@@ -109,6 +109,9 @@ stdenv.mkDerivation rec {
 
     # fix test output with sympy 1.7 (https://trac.sagemath.org/ticket/30985)
     ./patches/sympy-1.7-update.patch
+
+    # workaround until we use sage's fork of threejs, which contains a "version" file
+    ./patches/dont-grep-threejs-version-from-minified-js.patch
   ];
 
   patches = nixPatches ++ bugfixPatches ++ packageUpgradePatches;