Remove RUST_MIN_STACK declarations from CI scripts

.travis.yml

@@ -46,7 +46,7 @@ script:
   - |
     if [ -z ${INTEGRATION} ]; then
       cargo build
-      RUST_MIN_STACK=8388608 cargo test
+      cargo test
     else
       ./ci/integration.sh
     fi

appveyor.yml

@@ -2,7 +2,6 @@
 # and modified (mainly removal of deployment) to suit rustfmt.
 
 environment:
-  RUST_MIN_STACK: 8388608
   global:
     PROJECT_NAME: rustfmt
   matrix: