Bump go 1.13

Signed-off-by: Guillaume J. Charmes <gcharmes@magicleap.com>
diff --git a/Dockerfile.riscv b/Dockerfile.riscv
index 476d8f1..adfdf82 100644
--- a/Dockerfile.riscv
+++ b/Dockerfile.riscv
@@ -1,4 +1,4 @@
-FROM golang:1.12
+FROM golang:1.13
 
 # Clone and complie a riscv compatible version of the go compiler.
 RUN git clone https://review.gerrithub.io/riscv/riscv-go /riscv-go
diff --git a/go.mod b/go.mod
new file mode 100644
index 0000000..e48deca
--- /dev/null
+++ b/go.mod
@@ -0,0 +1,4 @@
+module github.com/creack/pty
+
+go 1.13
+