Ensure BUILDEVENTS_SPAN_ID (#73)

Ensures the BUILDEVENTS_SPAN_ID environment variable is set to the appropriate value by using double quotes rather than waiting for evaluation later and leaving it unset.

orb.yml

@@ -139,7 +139,7 @@ commands:
             # in case this is a bash env, be kind and export the buildevents path and span ID
             # this orb won't rely on them but consumers of the orb might find it useful
             # this way steps that are run within a span can use the raw buildevents if desired
-            echo 'export BUILDEVENTS_SPAN_ID=$BUILDEVENTS_SPAN_ID' >> $BASH_ENV
+            echo "export BUILDEVENTS_SPAN_ID=$BUILDEVENTS_SPAN_ID" >> $BASH_ENV
             if uname -a | grep Linux | grep x86_64 > /dev/null 2>&1 ; then
               echo 'export PATH=$PATH:/tmp/buildevents/be/bin-linux:/tmp/be/bin-linux' >> $BASH_ENV
             elif uname -a | grep Linux | grep -e arm64 -e aarch64 > /dev/null 2>&1 ; then