Pin tool versions using go modules

This pins down the versions of various tools used in the building,
testing, and linting of kustomize. This will provide more consistency
across contributors' and travis' environments.

travis/pre-commit.sh

@@ -14,24 +14,8 @@ function installHelm {
   sudo mv linux-amd64/helm /usr/local/bin/helm
 }
 
-function doInstall {
-  local tool=$1
-  shift
-  if hash $tool 2>/dev/null; then
-    echo "$tool available."
-  else
-    echo "Installing ${tool}..."
-    eval $@
-  fi
-}
-
 function installTools {
-  doInstall mdrip \
-    'go get -u github.com/monopole/mdrip'
-  doInstall golangci-lint \
-    'curl -sfL https://raw.githubusercontent.com/golangci/golangci-lint/master/install.sh | sh -s -- -b $(go env GOPATH)/bin v1.17.1'
-  doInstall pluginator \
-    'go install sigs.k8s.io/kustomize/pluginator'
+  go install sigs.k8s.io/kustomize/pluginator
 }
 
 function runFunc {
@@ -48,7 +32,7 @@ function runFunc {
 }
 
 function testGoLangCILint {
-  golangci-lint run ./...
+  go run "github.com/golangci/golangci-lint/cmd/golangci-lint" run ./...
 }
 
 function testGoTests {
@@ -80,7 +64,7 @@ function testExamplesAgainstLatestRelease {
   # Install latest release.
   go get sigs.k8s.io/kustomize/v3/cmd/kustomize
 
-  mdrip --mode test --label testAgainstLatestRelease ./examples
+  go run "github.com/monopole/mdrip" --mode test --label testAgainstLatestRelease ./examples
 
   if [ -z ${TRAVIS+x} ]; then
     echo " "
@@ -89,7 +73,7 @@ function testExamplesAgainstLatestRelease {
 
     # The following requires helm.
     # At the moment not asking travis to install it.
-    mdrip --mode test --label helmtest README.md ./examples/chart.md
+    go run "github.com/monopole/mdrip" --mode test --label helmtest README.md ./examples/chart.md
   fi
 }
 
@@ -100,7 +84,7 @@ function testExamplesAgainstHead {
   # To test examples of unreleased features, add
   # examples with code blocks annotated with some
   # label _other than_ @testAgainstLatestRelease.
-  mdrip --mode test --label testAgainstLatestRelease ./examples
+  go run "github.com/monopole/mdrip" --mode test --label testAgainstLatestRelease ./examples
 }
 
 function generateCode {