Fix (mathematical) typos in PCA documentation (#1045)
Fix (mathematical) typos in PCA documentation (#1045)

- correct formula for :math:`C_{y}`
- use :math:`\times` for matrix dimensions
- correct formula for eigenvector
- fix :math:`\over` with :math:`\frac{}{}`
- replace :math:`\sum` with :math:`\Sigma`
- fix missing ')' and misplaced '`' in 'SVD (locally)'
- add missing '='
- remove redundant parentheses for left singular vectors
mathemage/h2o-3,h2oai/h2o-3,mathemage/h2o-3,h2oai/h2o-dev,h2oai/h2o-3,h2oai/h2o-dev,michalkurka/h2o-3,michalkurka/h2o-3,h2oai/h2o-3,spennihana/h2o-3,h2oai/h2o-3,mathemage/h2o-3,spennihana/h2o-3,spennihana/h2o-3,h2oai/h2o-3,h2oai/h2o-dev,michalkurka/h2o-3,spennihana/h2o-3,h2oai/h2o-3,michalkurka/h2o-3,spennihana/h2o-3,michalkurka/h2o-3,h2oai/h2o-3,mathemage/h2o-3,h2oai/h2o-dev,h2oai/h2o-dev,michalkurka/h2o-3,mathemage/h2o-3,mathemage/h2o-3,spennihana/h2o-3,h2oai/h2o-3,mathemage/h2o-3,spennihana/h2o-3,h2oai/h2o-dev,h2oai/h2o-dev,michalkurka/h2o-3