update heapless create version up. to 0.6.1
If the version of heapless crate is 0.6.1 or less, there seems to be a security problem, so I upgraded the version.
https://www.cve.org/CVERecord?id=CVE-2020-36464
In addition, since it seems that the code needs to be corrected if it is the latest 0.7.13, it is temporarily updated to 0.6.1.