speed: fix build for Go 1.4 and lower

Old Go versions miss cipher.NewGCMWithNonceSize, which causes:

  internal/speed/speed.go:95: undefined: cipher.NewGCMWithNonceSize

1 files changed, 11 insertions, 0 deletions

diff --git a/internal/speed/speed_go1.4.go b/internal/speed/speed_go1.4.go
new file mode 100644
index 0000000..9c0125c
--- /dev/null
+++ b/internal/speed/speed_go1.4.go
@@ -0,0 +1,11 @@
+// +build !go1.5
+
+package speed
+
+import (
+	"fmt"
+)
+
+func Run() {
+	fmt.Printf("Compile with Go 1.5 or higher to run the benchmarks\n")
+}