tools: add double-quotes to make-v8.sh

Now that we maintain make-v8.sh rather than pull it from upstream, we
can make it conform to our shellcheck lint checks.

This is not being flagged in CI because (I'm guessing) shellcheck in CI
is 0.7.0 but latest is 0.8.0.

tools/make-v8.sh

@@ -17,7 +17,7 @@ if [ "$ARCH" = "s390x" ] || [ "$ARCH" = "ppc64le" ]; then
   fi
   # set paths manually for now to use locally installed gn
   export BUILD_TOOLS=/home/iojs/build-tools
-  export LD_LIBRARY_PATH=$BUILD_TOOLS:$LD_LIBRARY_PATH
+  export LD_LIBRARY_PATH="$BUILD_TOOLS:$LD_LIBRARY_PATH"
   # Avoid linking to ccache symbolic links as ccache decides which
   # binary to run based on the name of the link (we always name them gcc/g++).
   # shellcheck disable=SC2154
@@ -28,7 +28,7 @@ if [ "$ARCH" = "s390x" ] || [ "$ARCH" = "ppc64le" ]; then
   rm -f "$BUILD_TOOLS/gcc"
   ln -s "$CXX_PATH" "$BUILD_TOOLS/g++"
   ln -s "$CC_PATH" "$BUILD_TOOLS/gcc"
-  export PATH=$BUILD_TOOLS:$PATH
+  export PATH="$BUILD_TOOLS:$PATH"
 
   g++ --version
   gcc --version