title: $GOPATH is set but go install does not work
body: <p>I am trying to understand the go environment, but I can't seem to <code>go install</code> any package I git cloned locally. <code>go install</code> on the hello world example works fine.</p>
  
  <pre><code>~GOPATH/src/go-github(master ✔) go install -i go-github/github
  ~GOPATH/src/go-github(master ✔)
  ~GOPATH/src/go-github(master ✔)
  ~GOPATH/src/go-github(master ✔) ll ~GOBIN
  total 80992
  -rwxr-xr-x  1 drez  1896053708   6.2M Sep 21 14:57 basicauth
  -rwxr-xr-x  1 drez  1896053708   6.3M Sep 21 14:57 commitpr
  -rwxr-xr-x  1 drez  1896053708   6.3M Sep 21 14:57 fields
  -rwxr-xr-x  1 drez  1896053708   1.9M Sep 21 14:06 hello
  -rwxr-xr-x  1 drez  1896053708   6.2M Sep 21 14:57 migrations
  -rwxr-xr-x  1 drez  1896053708   6.3M Sep 21 14:57 newrepo
  -rwxr-xr-x  1 drez  1896053708   6.3M Sep 21 14:57 simple
  </code></pre>
  
  <p>My <code>go env</code> output is as follows:</p>
  
  <pre><code>~GOPATH/src/go-github(master ✔) go env
  GOARCH="amd64"
  GOBIN="/Users/drez/Dev/golang/bin"
  GOCACHE="/Users/drez/Library/Caches/go-build"
  GOEXE=""
  GOFLAGS=""
  GOHOSTARCH="amd64"
  GOHOSTOS="darwin"
  GOOS="darwin"
  GOPATH="/Users/drez/Dev/golang"
  GOPROXY=""
  GORACE=""
  GOROOT="/usr/local/go"
  GOTMPDIR=""
  GOTOOLDIR="/usr/local/go/pkg/tool/darwin_amd64"
  GCCGO="gccgo"
  CC="clang"
  CXX="clang++"
  CGO_ENABLED="1"
  GOMOD=""
  CGO_CFLAGS="-g -O2"
  CGO_CPPFLAGS=""
  CGO_CXXFLAGS="-g -O2"
  CGO_FFLAGS="-g -O2"
  CGO_LDFLAGS="-g -O2"
  PKG_CONFIG="pkg-config"
  GOGCCFLAGS="-fPIC -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/f7/zq9bg2ds6671wp4s7v3vkyf5rzyx5d/T/go-build744915712=/tmp/go-build -gno-record-gcc-switches -fno-common"
  </code></pre>
  
  <p>$PATH with $GOBIN at the end:</p>
  
  <pre><code>~GOPATH/src/go-github(master ✔) echo $PATH /Users/drez/.toolbox/bin:/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/go/bin:/Users/drez/.toolbox/bin:/Users/drez/Library/Android/sdk/platform-tools:/Library/Frameworks/Python.framework/Versions/3.6/bin:/Library/Frameworks/Python.framework/Versions/3.5/bin:/Users/drez/Library/Android/sdk/platform-tools:/Users/drez/Dev/golang/bin
  </code></pre>