Knobs: fix label alignment

[Hypnosphi]

Issue:
#1086 introduced increased font size for labels. Unfortunately, that broke alignment

What I did

Lowered the padding-top

How to test

Run any story with knobs addon

Before:

After:

[codecov]

Codecov Report

Merging #1471 into master will not change coverage.
The diff coverage is 0%.

@@           Coverage Diff           @@
##           master    #1471   +/-   ##
=======================================
  Coverage   14.34%   14.34%           
=======================================
  Files         201      201           
  Lines        4614     4614           
  Branches      503      497    -6     
=======================================
  Hits          662      662           
  Misses       3527     3527           
  Partials      425      425

Impacted Files	Coverage Δ
addons/knobs/src/components/types/Number.js	8.06% <ø> (ø)	⬆️
addons/knobs/src/components/PropField.js	10.86% <0%> (ø)	⬆️
app/react/src/server/babel_config.js	44.82% <0%> (ø)	⬆️
app/react/src/client/preview/client_api.js	39.28% <0%> (ø)	⬆️
app/react-native/src/bin/storybook-start.js	0% <0%> (ø)	⬆️
lib/ui/src/modules/api/configs/init_api.js	40.47% <0%> (ø)	⬆️
addons/info/src/components/Node.js	0% <0%> (ø)	⬆️
lib/ui/src/modules/ui/libs/filters.js	41.66% <0%> (ø)	⬆️
addons/knobs/src/components/WrapStory.js	12% <0%> (ø)	⬆️
.../ui/src/modules/ui/components/left_panel/header.js	28.57% <0%> (ø)	⬆️
... and 23 more

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[shilman]

Thanks @Hypnosphi looks great!!