use first commit from symengine/symengine#2129

Author: bjodah

appveyor.yml

@@ -74,6 +74,8 @@ install:
 
 - set /p commit=<symengine_version.txt
 - cd symengine-cpp
+- git config --add remote.origin.fetch "+refs/pull/*/head:refs/remotes/origin/pr/*"
+- git fetch
 - git checkout %commit%
 - mkdir build
 - cd build

bin/test_symengine_unix.sh

@@ -4,6 +4,8 @@ export MAKEFLAGS="-j2"
 
 git clone https://github.com/symengine/symengine symengine-cpp
 cd symengine-cpp
+git config --add remote.origin.fetch '+refs/pull/*/head:refs/remotes/origin/pr/*'
+git fetch
 export SOURCE_DIR=`pwd`
 git checkout `cat ../symengine_version.txt`
 cd ..

symengine_version.txt

@@ -1 +1 @@
-8a3bc848cd8246a4c15eee9bddc15de0d1157812
+b9b11156a76470f0e6998476b2550573efdb5aae