build(java): readme.sh should be executable (#1137)

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Source-Link: googleapis/synthtool@0762e8e

Author: yoshi-automation

.kokoro/readme.sh

@@ -4,14 +4,14 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/google-http-java-client.git",
-        "sha": "3a756393060021afe028d315fc023b74d2479943"
+        "sha": "fe73acdd345ae3a2d7f214bec0058a6c0a122a7d"
       }
     },
     {
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "8a7a3021fe97aa0a3641db642fe2b767f1c8110f"
+        "sha": "0762e8ee2ec21cdfc4d82020b985a104feb0453b"
       }
     }
   ],