String Formatting and PEP-8 fixes

[vkmrishad]

Fixes #109

Checklist

• [x] I have made a material change to the repo (functionality, testing, spelling, grammar)
• [x] I have read the [Contribution Guide] and my PR follows them.
• [x] I updated my branch with the master branch.
• [x] I have added tests that prove my fix is effective or that my feature works
• [ ] I have added necessary documentation about the functionality in the appropriate .md file
• [ ] I have added inline documentation to the code I modified

Short description of what this PR does:

• PEP8 fix in ReadMe file
• String formatting enhancement.

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[SendGridDX]

All committers have signed the CLA.

[codecov[bot]]

Codecov Report

Merging #109 into master will decrease coverage by 24.22%. The diff coverage is 80%.

@@             Coverage Diff             @@
##           master     #109       +/-   ##
===========================================
- Coverage   91.34%   67.12%   -24.23%     
===========================================
  Files           6        6               
  Lines         289      289               
===========================================
- Hits          264      194       -70     
- Misses         25       95       +70

Impacted Files	Coverage Δ
tests/test_repofiles.py	100% <ø> (ø)	:arrow_up:
tests/test_unit.py	69.59% <100%> (-29.61%)	:arrow_down:
python_http_client/client.py	54.36% <50%> (-23.31%)	:arrow_down:
python_http_client/exceptions.py	73.68% <0%> (-23.69%)	:arrow_down:

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