Update tests to work with go 1.10+ (#73)

Fixes #72

Author: belak

circle.yml

@@ -2,7 +2,7 @@ version: 2.0
 jobs:
   build:
     docker:
-    - image: golang:1.8
+    - image: golang:1.10
     working_directory: /go/src/github.com/gliderlabs/ssh
     steps:
     - checkout

session_test.go

@@ -219,7 +219,7 @@ func TestPty(t *testing.T) {
 	}, nil)
 	defer cleanup()
 	if err := session.RequestPty(term, winHeight, winWidth, gossh.TerminalModes{}); err != nil {
-		t.Fatalf("unexpected error requesting PTY", err)
+		t.Fatalf("expected nil but got %v", err)
 	}
 	if err := session.Shell(); err != nil {
 		t.Fatalf("expected nil but got %v", err)
@@ -252,7 +252,7 @@ func TestPtyResize(t *testing.T) {
 	defer cleanup()
 	// winch0
 	if err := session.RequestPty("xterm", winch0.Height, winch0.Width, gossh.TerminalModes{}); err != nil {
-		t.Fatalf("unexpected error requesting PTY", err)
+		t.Fatalf("expected nil but got %v", err)
 	}
 	if err := session.Shell(); err != nil {
 		t.Fatalf("expected nil but got %v", err)