Truncate Gradle args when constructing cache key (#71)

Cache keys have a hard limit of 512 characters, so we need to ensure that we don't generate a key longer than this.

- Remove excess whitespace
- Truncate to 400 characters

Fixes #70

src/cache-utils.ts

@@ -0,0 +1,17 @@
+import * as path from 'path'
+import * as glob from '@actions/glob'
+
+export async function hashFiles(
+    baseDir: string,
+    patterns: string[] = ['**'],
+    followSymbolicLinks = false
+): Promise<string | null> {
+    const combinedPatterns = patterns
+        .map(pattern => `${baseDir}${path.sep}${pattern}`)
+        .join('\n')
+    return glob.hashFiles(combinedPatterns, {followSymbolicLinks})
+}
+
+export function truncateArgs(args: string): string {
+    return args.trim().replace(/\s+/g, ' ').substr(0, 400)
+}