Fix to the syntax warnings caused by comparing literals

[ilkericyuz]

What current issue(s) does this address, or what feature is it adding? There are 5 syntax warnings in 2 files in the current code. Warnings appear when neo-python is installed as a library in a separate project.

SyntaxWarning: "is not" with a literal. Did you mean "!="?

How did you solve this problem? Replaced them with != which is the proper way to compare literals.

How did you make sure your solution works? It doesn't raise syntax warning anymore.

Are there any special changes in the code that we should be aware of? no

Please check the following, if applicable:

• [ ] Did you add any tests? n/a
• [x] Did you run make lint?
• [x] Did you run make test?
• [x] Are you making a PR to a feature branch or development rather than master?
• [x] Did you add an entry to CHANGELOG.rst? (if not, please do)

[ixje]

Thanks!

[coveralls]

Coverage remained the same at 85.312% when pulling 074b31d067267ec860bee267e33a25b8813570d7 on bitpanda-labs:syntax-warnings-fix into a7f8392c01104d43008edbc669374c9f1bbdcf0d on CityOfZion:development.