go version command shows old version number after update to 1.8

In my case, I had to replace binary files manually after re-installation.

cp /usr/local/go/bin/* /usr/local/bin/

I had the same issue. Even after installing golang 1.10 on mac through download from golang website, mac terminal still showed 1.7 version.

Updating golang through homebrew fixed my issue.

brew update
brew upgrade golang

You obviously have an old version of Go installed, else you couldn't see go version go1.7.5 darwin/amd64 as the output of go version.

IDEs might have more advanced method of detecting Go installations other that simply scanning PATH and GOROOT (and that's why your IDE found and suggested the newer Go 1.8).

Execute which go, and you'll see where your old Go resides. Remove it (and references to it).

Note that in your .bashrc you're appending the proper Go bin folder to the end of PATH:

export PATH=$PATH:/usr/local/go/bin

Which means if PATH contains the bin folder of the old Go installation (very likely), that is used to execute the go command.