Try a different install directory of sbt

sbt/sbt#5587

Author: liufengyun

.appveyor.yml

@@ -8,8 +8,8 @@ matrix:
 
 init:
   - ps: Install-Product node $env:NODEJS_VERSION
-  - cmd: choco install sbt --version 1.3.12
-  - cmd: refreshenv
+  - cmd: choco install sbt --version 1.3.12 -ia "INSTALLDIR=""C:\sbt"""
+  - cmd: SET PATH=C:\sbt\bin;%PATH%
   - cmd: SET "SBT_OPTS=-Xmx4g -Xms4m"
 build_script:
   - cmd: sbt dotty-bootstrapped/compile