install-minion script doesn't hardcode the compiler version

.travis.yml

@@ -75,7 +75,7 @@ install:
   - savilerow | head -n2 | tail -n1          # print version
 
   # Minion
-  - (minion | grep 'Minion Version 2') || etc/build/install-minion.sh
+  - (minion | grep 'Minion Version 2') || (COMPILER="g++-4.9" etc/build/install-minion.sh)
   - minion help | head -n2                   # print version
 
   # Lingeling

etc/build/install-minion.sh

@@ -4,17 +4,25 @@ set -o errexit
 set -o nounset
 
 export BIN_DIR=${BIN_DIR:-${HOME}/.cabal/bin}
+export COMPILER=${COMPILER:-""}
 
 rm -rf ~/tmp-install-minion
 mkdir ~/tmp-install-minion
 pushd ~/tmp-install-minion
 hg clone https://bitbucket.org/stacs_cp/minion
 mkdir -p minion/build
-COMPILER="g++-4.9"
-if which ccache; then
-    COMPILER="ccache ${COMPILER}"
-fi
-(cd minion/build && ../build.py --compiler "${COMPILER}" && make minion -j2)
+(
+    cd minion/build
+    if [ -z "${COMPILER}" ]; then
+        ../build.py
+    else
+        if which ccache; then
+            COMPILER="ccache ${COMPILER}"
+        fi
+        ../build.py --compiler "${COMPILER}"
+    fi
+    make minion -j2
+)
 cp minion/build/minion ${BIN_DIR}/minion
 echo "minion executable is at ${BIN_DIR}/minion"
 ls -l ${BIN_DIR}/minion