Eigen 3.4.1 may have been too aggressive for windows

Trying 3.4.0

Author: SeanCurtis-TRI

.appveyor.yml

@@ -38,9 +38,9 @@ before_build:
             cd ..\..
          ) else (echo Using cached libccd)
   - cmd: if not exist C:\"Program Files"\Eigen\include\eigen3\Eigen\Core (
-            curl -LO https://gitlab.com/libeigen/eigen/-/archive/3.4.1/eigen-3.4.1.tar.gz &&
-            cmake -E tar zxf eigen-3.4.1.tar.gz &&
-            cd eigen-3.4.1 &&
+            curl -LO https://gitlab.com/libeigen/eigen/-/archive/3.4.0/eigen-3.4.0.tar.gz &&
+            cmake -E tar zxf eigen-3.4.0.tar.gz &&
+            cd eigen-3.4.0 &&
             mkdir build &&
             cd build &&
             cmake -G "%CMAKE_GENERATOR_NAME%" -DCMAKE_BUILD_TYPE=%Configuration% .. &&