Update release_notes.txt

Author: barkz

release_notes.txt

@@ -1,4 +1,4 @@
-Pure Storage PowerShell SDK 1.6 Release Notes
+Pure Storage PowerShell SDK 1.7.4.0 Release Notes
 
 The Pure Storage PowerShell SDK provides integration with the Purity Operating Environment and FlashArray. It provides functionalities of Purity's REST API as PowerShell cmdlets.
 
@@ -100,4 +100,4 @@ FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
-SOFTWARE.
+SOFTWARE.