Update the Java launcher

[puffnfresh]

Includes some fixes like using /usr/bin/env instead of /bin/bash which
makes apps work on weird systems, like mine.

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[puffnfresh]

Tests previously failed with:

rules_kotlin/src/test/kotlin/io/bazel/kotlin/KotlinJvmFriendsVisibilityTest: /bin/bash: bad interpreter: No such file or directory

Now pass with:

//src/test/kotlin/io/bazel/kotlin:KotlinJvmFriendsVisibilityTest         PASSED in 0.5s

[puffnfresh]

@googlebot I signed it!

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[jin]

cc @djwhang