Remove secureexec package

From the go 1.19 release notes:

Command and LookPath no longer allow results from a PATH search to be found relative to the current directory. This removes a common source of security problems but may also break existing programs that depend on using, say, exec.Command("prog") to run a binary named prog (or, on Windows, prog.exe) in the current directory. See the os/exec package documentation for information about how best to update such programs.

Dockerfile

@@ -2,7 +2,7 @@
 # docker build -t lazygit .
 # docker run -it lazygit:latest /bin/sh
 
-FROM golang:1.18 as build 
+FROM golang:1.20 as build
 WORKDIR /go/src/github.com/jesseduffield/lazygit/
 COPY go.mod go.sum ./
 RUN go mod download