appveyor:  update test matrix for go1.14
MODIFY
appveyor.yml
appveyor.yml
@@ -13,8 +13,8 @@ environment:
# Do not move these lines; they are referred to by README.md.
# Versions of go that are explicitly supported by gonum.
matrix:
- - GOROOT: 'c:\go112'
- #- GOROOT: 'c:\go113'
+ - GOROOT: 'c:\go113'
+ #- GOROOT: 'c:\go114'
GOPATH: c:\gopath
GOTOOLDIR: '%GOROOT%\pkg\tool\windows_amd64'
PATH: '%GOPATH%\bin;%GOROOT%\bin;%PATH%'

appveyor:  update test matrix for go1.14