build(deps): bump posix-spawn from 0.3.13 to 0.3.15

Bumps [posix-spawn](https://github.com/rtomayko/posix-spawn) from 0.3.13 to 0.3.15.
- [Release notes](https://github.com/rtomayko/posix-spawn/releases)
- [Commits](rtomayko/posix-spawn@v0.3.13...v0.3.15)

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

Gemfile

@@ -25,7 +25,7 @@ gem 'netaddr', '>= 2.0.4'
 gem 'newrelic_rpm'
 gem 'nokogiri', '>=1.10.5'
 gem 'palm_civet'
-gem 'posix-spawn', '~> 0.3.6'
+gem 'posix-spawn', '~> 0.3.15'
 gem 'protobuf', '3.6.12'
 gem 'public_suffix'
 gem 'rake'

Gemfile.lock

@@ -304,7 +304,7 @@ GEM
     parser (2.7.1.4)
       ast (~> 2.4.1)
     pg (1.2.3)
-    posix-spawn (0.3.13)
+    posix-spawn (0.3.15)
     protobuf (3.6.12)
       activesupport (>= 3.2)
       middleware
@@ -538,7 +538,7 @@ DEPENDENCIES
   palm_civet
   parallel_tests
   pg
-  posix-spawn (~> 0.3.6)
+  posix-spawn (~> 0.3.15)
   protobuf (= 3.6.12)
   pry-byebug
   public_suffix