build(java): readme.sh should be executable (googleapis#247)

This PR was generated using Autosynth. 🌈 Synth log will be available here: https://source.cloud.google.com/results/invocations/1ba237d2-34b1-461d-898e-5656d73dd597/targets - [ ] To automatically regenerate this PR, check this box. Source-Link: googleapis/synthtool@0762e8e

Author: yoshi-automation

.kokoro/readme.sh

@@ -4,7 +4,7 @@
  "git": {
  "name": ".",
  "remote": "https://github.com/googleapis/java-tasks.git",
- "sha": "e20c1510307bddb844230f874762be0ba5ba73d8"
+ "sha": "15b2a3a27509459e5503080482d2d1588b57472f"
  }
  },
  {
@@ -19,7 +19,7 @@
  "git": {
  "name": "synthtool",
  "remote": "https://github.com/googleapis/synthtool.git",
- "sha": "8a7a3021fe97aa0a3641db642fe2b767f1c8110f"
+ "sha": "0762e8ee2ec21cdfc4d82020b985a104feb0453b"
  }
  }
  ],