Remove extra / in git commands in README

This works, but is usually not how it's written. A command later in the
README was already using this style.

Author: steveklabnik

README.md

@@ -66,15 +66,15 @@ compiler for C++14 support and create a symlink:
 
 ### Getting Sources for Swift and Related Projects
 
-     git clone git@github.com:/apple/swift.git swift
-     git clone git@github.com:/apple/swift-llvm.git llvm
-     git clone git@github.com:/apple/swift-clang.git clang
-     git clone git@github.com:/apple/swift-lldb.git lldb
-     git clone git@github.com:/apple/swift-cmark.git cmark
-     git clone git@github.com:/apple/swift-llbuild.git llbuild
-     git clone git@github.com:/apple/swift-package-manager.git swiftpm
-     git clone git@github.com:/apple/swift-corelibs-xctest.git 
-     git clone git@github.com:/apple/swift-corelibs-foundation.git 
+     git clone git@github.com:apple/swift.git swift
+     git clone git@github.com:apple/swift-llvm.git llvm
+     git clone git@github.com:apple/swift-clang.git clang
+     git clone git@github.com:apple/swift-lldb.git lldb
+     git clone git@github.com:apple/swift-cmark.git cmark
+     git clone git@github.com:apple/swift-llbuild.git llbuild
+     git clone git@github.com:apple/swift-package-manager.git swiftpm
+     git clone git@github.com:apple/swift-corelibs-xctest.git
+     git clone git@github.com:apple/swift-corelibs-foundation.git
 
 
 [CMake](http://cmake.org) is the core infrastructure used to configure builds of
@@ -141,4 +141,4 @@ See [docs/Testing.rst](docs/Testing.rst).
 
 ## Contributing to Swift
 
-Contributions to Swift are welcomed and encouraged! Please see the [Contributing to Swift guide](https://swift.org/contributing/).
+Contributions to Swift are welcomed and encouraged! Please see the [Contributing to Swift guide](https://swift.org/contributing/).