Fix lint check obsolete warning

[ShaishavGandhi]

No description provided.

[TWiStErRob]

Ref: this is a regression of #1074 with a newer version:

butterknife-runtime-10.1.0.aar...\lint.jar: Lint found an issue registry (butterknife.lint.LintRegistry) which is older than the current API level; these checks may not work correctly.
Recompile the checks against the latest version. Custom check API version is 2 (3.2), current lint API level is 3 (3.3+)

@shaishavgandhi05 please add minApi to butterknife/lint/LintRegistry.java:

@Override public int getMinApi() {
    return 2;
}

Reason: we know this lint check is compatible with 2 and 3, compiling with 3 is good as it'll make sure this warning goes, but 2 should also be supported, otherwise this PR just moves the warning from one AGP version to another.