update docs to match pytest master/worker terminology

README.rst

@@ -139,9 +139,9 @@ examine it.
 Limitations
 ===========
 
-For distributed testing the slaves must have the pytest-cov package installed.  This is needed since
+For distributed testing the workers must have the pytest-cov package installed.  This is needed since
 the plugin must be registered through setuptools for pytest to start the plugin on the
-slave.
+worker.
 
 For subprocess measurement environment variables must make it from the main process to the
 subprocess.  The python used by the subprocess must have pytest-cov installed.  The subprocess must

docs/xdist.rst

@@ -5,9 +5,9 @@ Distributed testing (xdist)
 "load" mode
 ===========
 
-Distributed testing with dist mode set to load will report on the combined coverage of all slaves.
-The slaves may be spread out over any number of hosts and each slave may be located anywhere on the
-file system.  Each slave will have its subprocesses measured.
+Distributed testing with dist mode set to load will report on the combined coverage of all workers.
+The workers may be spread out over any number of hosts and each worker may be located anywhere on the
+file system.  Each worker will have its subprocesses measured.
 
 Running distributed testing with dist mode set to load::
 
@@ -48,8 +48,8 @@ Shows a terminal report::
 "each" mode
 ===========
 
-Distributed testing with dist mode set to each will report on the combined coverage of all slaves.
-Since each slave is running all tests this allows generating a combined coverage report for multiple
+Distributed testing with dist mode set to each will report on the combined coverage of all workers.
+Since each worker is running all tests this allows generating a combined coverage report for multiple
 environments.
 
 Running distributed testing with dist mode set to each::