[install] Build fzf if prebuilt binary doesn't work

Close #617

install

@@ -9,6 +9,7 @@ auto_completion=
 key_bindings=
 update_config=2
 binary_arch=
+allow_legacy=
 
 help() {
   cat << EOF
@@ -37,6 +38,7 @@ for opt in "$@"; do
       auto_completion=1
       key_bindings=1
       update_config=1
+      allow_legacy=1
       ;;
     --key-bindings)    key_bindings=1    ;;
     --no-key-bindings) key_bindings=0    ;;
@@ -165,6 +167,9 @@ case "$archi" in
 esac
 
 install_ruby_fzf() {
+  if [ -z "$allow_legacy" ]; then
+    ask "Do you want to install legacy Ruby version instead?" && exit 1
+  fi
   echo "Installing legacy Ruby version ..."
 
   # ruby executable
@@ -236,26 +241,25 @@ cd "$fzf_base"
 if [ -n "$binary_error" ]; then
   if [ $binary_available -eq 0 ]; then
     echo "No prebuilt binary for $archi ..."
-    if command -v go > /dev/null; then
-      echo -n "Building binary (go get -u github.com/junegunn/fzf/src/fzf) ... "
-      if [ -z "${GOPATH-}" ]; then
-        export GOPATH="${TMPDIR:-/tmp}/fzf-gopath"
-        mkdir -p "$GOPATH"
-      fi
-      if go get -u github.com/junegunn/fzf/src/fzf; then
-        echo "OK"
-        cp "$GOPATH/bin/fzf" "$fzf_base/bin/"
-      else
-        echo "Failed to build binary ..."
-        install_ruby_fzf
-      fi
+  else
+    echo "  - $binary_error !!!"
+  fi
+  if command -v go > /dev/null; then
+    echo -n "Building binary (go get -u github.com/junegunn/fzf/src/fzf) ... "
+    if [ -z "${GOPATH-}" ]; then
+      export GOPATH="${TMPDIR:-/tmp}/fzf-gopath"
+      mkdir -p "$GOPATH"
+    fi
+    if go get -u github.com/junegunn/fzf/src/fzf; then
+      echo "OK"
+      cp "$GOPATH/bin/fzf" "$fzf_base/bin/"
     else
-      echo "go executable not found. Cannot build binary ..."
+      echo "Failed to build binary ..."
       install_ruby_fzf
     fi
   else
-    echo "  - $binary_error !!!"
-    exit 1
+    echo "go executable not found. Cannot build binary ..."
+    install_ruby_fzf
   fi
 fi