Auth libraries dependency problem fix

[vam-google]

googleapis/google-cloud-java#2050

[garrettjonesgoogle]

LGTM

[codecov-io]

Codecov Report

Merging #310 into master will decrease coverage by 0.05%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master     #310      +/-   ##
============================================
- Coverage     69.98%   69.93%   -0.06%     
  Complexity      352      352              
============================================
  Files            72       72              
  Lines          1906     1906              
  Branches        155      155              
============================================
- Hits           1334     1333       -1     
- Misses          505      506       +1     
  Partials         67       67

Impacted Files	Coverage Δ	Complexity Δ
...java/com/google/api/gax/grpc/RetryingCallable.java	85.18% <0%> (-1.86%)	6% <0%> (ø)

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[shinfan]

LGTM

io.grpc:grpc-auth:1.2.0 is also depending on 0.4.0. We may need to ask the gRPC team to update as well.