Bump version strings post release (#6722)

Now that qiskit-terra 0.18.0 is out the door we should bump the version
string on master to show the source version we're installing is newer
than what's been released.

.mergify.yml

@@ -20,4 +20,4 @@ pull_request_rules:
     actions:
       backport:
         branches:
-          - stable/0.17
+          - stable/0.18

docs/conf.py

@@ -45,7 +45,7 @@ author = "Qiskit Development Team"
 # The short X.Y version
 version = ""
 # The full version, including alpha/beta/rc tags
-release = "0.18.0"
+release = "0.19.0"
 
 # -- General configuration ---------------------------------------------------
 

qiskit/VERSION.txt

@@ -1 +1 @@
-0.18.0
+0.19.0

setup.py

@@ -99,7 +99,7 @@ bip_requirements = ["cplex", "docplex"]
 
 setup(
     name="qiskit-terra",
-    version="0.18.0",
+    version="0.19.0",
     description="Software for developing quantum computing programs",
     long_description=README,
     long_description_content_type="text/markdown",