MINOR: trim environment variable values

When working on #78, I was hit by a test failing on linux (debian host)
Our code is triming values so we need to adjust the test code to make
sure we also trim values before doing the comparison.

Example:
```
	expected: "${debian_chroot:+($debian_chroot)}\\u@\\h:\\w\\$ "
	            	actual: "${debian_chroot:+($debian_chroot)}\\u@\\h:\\w\\$"
```

sigar_interface_test.go

@@ -5,6 +5,7 @@ import (
 	"os/user"
 	"path/filepath"
 	"runtime"
+	"strings"
 	"testing"
 	"time"
 
@@ -134,7 +135,7 @@ func TestProcEnv(t *testing.T) {
 		assert.True(t, len(env.Vars) > 0, "env is empty")
 
 		for k, v := range env.Vars {
-			assert.Equal(t, os.Getenv(k), v)
+			assert.Equal(t, strings.TrimSpace(os.Getenv(k)), v)
 		}
 	}
 }