Improve check for version string in svn --version

Author: deveshks

news/7968.bugfix

@@ -0,0 +1 @@
+Look for version string in the entire output of svn --version, not just the first line

src/pip/_internal/vcs/subversion.py

@@ -25,7 +25,7 @@
 
 
 if MYPY_CHECK_RUNNING:
-    from typing import Optional, Tuple
+    from typing import Optional, Tuple, Text
     from pip._internal.utils.subprocess import CommandArgs
     from pip._internal.utils.misc import HiddenText
     from pip._internal.vcs.versioncontrol import AuthInfo, RevOptions
@@ -215,7 +215,17 @@ def call_vcs_version(self):
         #   svn, version 1.7.14 (r1542130)
         #      compiled Mar 28 2018, 08:49:13 on x86_64-pc-linux-gnu
         version_prefix = 'svn, version '
-        version = self.run_command(['--version'], show_stdout=False)
+        cmd_output = self.run_command(['--version'], show_stdout=False)
+
+        # Split the output by newline, and find the line where
+        # version_prefix is present
+        output_lines = cmd_output.split('\n')
+        version = ''  # type: Text
+
+        for line in output_lines:
+            if version_prefix in line:
+                version = line
+
         if not version.startswith(version_prefix):
             return ()