Fix slowness by using ./project/scripts/sbt instead of sbt

@allanrenucci before that sbt ran without the -Dsbt.ivy.home option set and
the dependencies where downloaded again...

Author: OlivierBlanvillain

project/scripts/cmdTests

@@ -95,7 +95,7 @@ mkdir -p _site && ./bin/dotd -project Hello -siteroot _site tests/run/hello.scal
 
 echo "running Vulpix meta test"
 tmp=$(mktemp)
-if sbt -no-colors "dotty-compiler/testOnly dotty.tools.vulpix.VulpixMetaTests" > "$tmp" 2>&1; then
+if ./project/scripts/sbt -no-colors "dotty-compiler/testOnly dotty.tools.vulpix.VulpixMetaTests" > "$tmp" 2>&1; then
   echo "failed: sbt exited without error on VulpixMetaTests, these tests are expected to fail"
   exit -1
 fi