Upgrade custom-checkout plugin to version 1.8.0 (#46)

Author: ivannalisetska

README.md

@@ -22,7 +22,7 @@ steps:
   - label: "Skip checkout"
     command: 'echo "Skipping checkout"'
     plugins:
-      - custom-checkout#v1.7.0:
+      - custom-checkout#v1.8.0:
           skip_checkout: true
 ```
 
@@ -33,7 +33,7 @@ steps:
   - label: "Custom repository checkout"
     command: "buildkite-agent pipeline upload"
     plugins:
-      - custom-checkout#v1.7.0:
+      - custom-checkout#v1.8.0:
           skip_checkout: true
           repos:
             - url: "https://github.com/org/repo.git"
@@ -74,7 +74,7 @@ steps:
   - label: "Skip checkout"
     command: 'echo "Skipping checkout"'
     plugins:
-      - custom-checkout#v1.7.0:
+      - custom-checkout#v1.8.0:
           skip_checkout: true
 ```
 
@@ -85,7 +85,7 @@ steps:
   - label: "Custom checkout"
     command: "buildkite-agent pipeline upload"
     plugins:
-      - custom-checkout#v1.7.0:
+      - custom-checkout#v1.8.0:
           skip_checkout: true
           repos:
             - url: "https://github.com/org/repo.git"
@@ -98,7 +98,7 @@ steps:
   - label: "Multiple repos"
     command: "./script.sh"
     plugins:
-      - custom-checkout#v1.7.0:
+      - custom-checkout#v1.8.0:
           skip_checkout: true
           repos:
             - url: "https://github.com/org/repo1.git"
@@ -114,7 +114,7 @@ steps:
   - label: "Custom paths"
     command: "./script.sh"
     plugins:
-      - custom-checkout#v1.7.0:
+      - custom-checkout#v1.8.0:
           skip_checkout: true
           repos:
             - url: "https://github.com/org/repo1.git"
@@ -132,7 +132,7 @@ steps:
   - label: "Checkout with mirror"
     command: "buildkite-agent pipeline upload"
     plugins:
-      - custom-checkout#v1.7.0:
+      - custom-checkout#v1.8.0:
           skip_checkout: true
           repos:
             - url: "https://github.com/org/repo.git"
@@ -147,7 +147,7 @@ steps:
   - label: "Shallow clone with fetch"
     command: "buildkite-agent pipeline upload"
     plugins:
-      - custom-checkout#v1.7.0:
+      - custom-checkout#v1.8.0:
           skip_checkout: true
           repos:
             - url: "https://github.com/org/repo.git"