Revert version number to 0.7.6 (#993)

PR #984 incorrectly bumped the version number to 0.7.7, and I didn't
notice it during review. This PR changes the version back to 0.7.6,
which is the current development version in the main branch on GitHub.

Author: mhucka

release/setup.py

@@ -31,7 +31,7 @@
 from setuptools.command.install import install
 from setuptools.dist import Distribution
 
-CUR_VERSION = "0.7.7"
+CUR_VERSION = "0.7.6"
 
 DOCLINES = __doc__.split("\n")
 

tensorflow_quantum/__init__.py

@@ -64,4 +64,4 @@
 del core
 # pylint: enable=undefined-variable
 
-__version__ = '0.7.7'
+__version__ = '0.7.6'