build(java): readme.sh should be executable (#164)

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Source-Link: googleapis/synthtool@0762e8e

synth.metadata

@@ -4,7 +4,7 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/java-grafeas.git",
-        "sha": "2feef4d4e46ef2b2a6f93ccead609a79ef39f0f5"
+        "sha": "569addef56ff9a4169d217bf904f967a1337271b"
       }
     },
     {
@@ -19,7 +19,7 @@
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "e6168630be3e31eede633ba2c6f1cd64248dec1c"
+        "sha": "0762e8ee2ec21cdfc4d82020b985a104feb0453b"
       }
     }
   ],