Fix issues in scripts identified using shellcheck

contrib/completions/gen_completions

@@ -4,5 +4,5 @@
 set -e
 
 echo "Generating all completions using cargo debug binary..."
-cargo run -q -- generate completions all --output $PWD
+cargo run -q -- generate completions all --output "$PWD"
 echo "Done."

pkg/create_deb

@@ -9,13 +9,13 @@ if [[ ! $TRAVIS_TAG =~ ^v([0-9]+\.)*[0-9]+$ ]]; then
 fi
 
 # Ensure the debian architecture is set
-if [[ -z "$DEB_ARCH" ]]; then
+if [[ -z $DEB_ARCH ]]; then
     echo "Error: debian architecture not configured in \$DEB_ARCH"
     exit 1
 fi
 
 # Define some useful variables
-DIR="$( cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd )"
+DIR=$( cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd )
 VERSION=${TRAVIS_TAG:1}
 
 # Ensure the binary file exists
@@ -25,23 +25,23 @@ if [[ ! -f "$DIR/../ffsend" ]]; then
 fi
 
 # Create an application directory, copy the binary into it
-mkdir -p $DIR/ffsend-$VERSION
-cp $DIR/../ffsend $DIR/ffsend-$VERSION/ffsend
+mkdir -p "$DIR/ffsend-$VERSION"
+cp -- "$DIR/../ffsend" "$DIR/ffsend-$VERSION/ffsend"
 
 # Create an application tarbal
-cd $DIR/..
-git archive --format tar.gz -o $DIR/ffsend-$VERSION/ffsend-$VERSION.tar.gz $TRAVIS_TAG
+cd -- "$DIR/.."
+git archive --format tar.gz -o "$DIR/ffsend-$VERSION/ffsend-$VERSION.tar.gz" "$TRAVIS_TAG"
 
 # Change into the app directory
-cd $DIR/ffsend-$VERSION
+cd -- "$DIR/ffsend-$VERSION"
 
 # Build the debian package
 # TODO: define GPG?
-dh_make -e "timvisee@gmail.com" -c gpl3 -f ffsend-$VERSION.tar.gz -s -y
-rm *.ex README.Debian README.source
+dh_make -e "timvisee@gmail.com" -c gpl3 -f "ffsend-$VERSION.tar.gz" -s -y
+rm -- *.ex README.Debian README.source
 
 # Remove the project tar ball, we're not using it anymore
-rm $DIR/ffsend-$VERSION/ffsend-$VERSION.tar.gz
+rm -- "$DIR/ffsend-$VERSION/ffsend-$VERSION.tar.gz"
 
 # TODO: configure the debian/control file
 # TODO: configure copyright file