updating circom version to v2.2.1

[Chengxuan]

This PR updated the circom version to v2.2.1 for #100:

• Increased PTAU size to adopt the default fast simplification as it significantly reduces the circuit compilation time. More details here: https://github.com/iden3/circom/blob/master/mkdocs/docs/circom-language/circom-insight/simplification.md
• fixed the types of several test data for stricter type check
• updated gen.js concurrency to avoid overloading the CPU which makes the compiling less efficient

[Chengxuan]

using fast simplification, the circuit asset generation reduced from 42 mins to 18 mins:
before:

this PR:

[jimthematrix]

great to see the improvement in the proving key generation time!