Add addPath to core (#13)

* Add add-path

* Format

* lint

src/core.ts

@@ -1,6 +1,8 @@
 import {ExitCode} from '@actions/exit'
 import {issue, issueCommand} from './command'
 
+import * as path from 'path'
+
 /**
  * Interface for getInput options
  */
@@ -33,6 +35,15 @@ export function exportSecret(name: string, val: string): void {
   issueCommand('set-secret', {}, val)
 }
 
+/**
+ * Prepends inputPath to the PATH (for this action and future actions)
+ * @param inputPath
+ */
+export function addPath(inputPath: string): void {
+  issueCommand('add-path', {}, inputPath)
+  process.env['PATH'] = `${inputPath}${path.delimiter}${process.env['PATH']}`
+}
+
 /**
  * Gets the value of an input.  The value is also trimmed.
  *