Excavator: Update conjure plugins and dependencies (#573)

Author: svc-excavator-bot

versions.lock

@@ -12,7 +12,7 @@ com.github.zafarkhaja:java-semver:0.9.0 (1 constraints: 0b050636)
 com.google.code.findbugs:jsr305:3.0.2 (1 constraints: 980fcc86)
 com.google.errorprone:error_prone_annotations:2.6.0 (2 constraints: f320b156)
 com.google.guava:guava:21.0 (3 constraints: f528d884)
-com.palantir.conjure.java:conjure-lib:5.50.0 (1 constraints: 3c05513b)
+com.palantir.conjure.java:conjure-lib:5.51.0 (1 constraints: 3d05543b)
 com.palantir.conjure.java.api:errors:2.16.2 (1 constraints: 23109ea9)
 com.palantir.conjure.java.runtime:conjure-java-jackson-serialization:4.18.1 (1 constraints: 4005543b)
 com.palantir.ri:resource-identifier:1.1.0 (1 constraints: ea0f6899)

versions.props

@@ -11,8 +11,8 @@ org.mockito:mockito-core = 1.9.5
 org.slf4j:* = 1.7.12
 one.util:streamex = 0.7.2
 org.assertj:assertj-core = 3.14.0
-com.palantir.conjure:conjure = 4.14.2
-com.palantir.conjure.java:* = 5.50.0
+com.palantir.conjure:conjure = 4.15.2
+com.palantir.conjure.java:* = 5.51.0
 com.fasterxml.jackson.dataformat:* = 2.10.2
 one.util:streamex = 0.7.2
 com.github.tomakehurst:wiremock = 2.24.0